Revert "Improve iOS PlatformViews to better handle thread merging. (#16935)" (#17600)

This reverts commit f6b8eda7.

ci/licenses_golden/licenses_flutter

@@ -592,8 +592,6 @@ FILE: ../../../flutter/shell/common/shell_io_manager.cc
 FILE: ../../../flutter/shell/common/shell_io_manager.h
 FILE: ../../../flutter/shell/common/shell_test.cc
 FILE: ../../../flutter/shell/common/shell_test.h
-FILE: ../../../flutter/shell/common/shell_test_external_view_embedder.cc
-FILE: ../../../flutter/shell/common/shell_test_external_view_embedder.h
 FILE: ../../../flutter/shell/common/shell_test_platform_view.cc
 FILE: ../../../flutter/shell/common/shell_test_platform_view.h
 FILE: ../../../flutter/shell/common/shell_test_platform_view_gl.cc

flow/embedded_views.h

@@ -253,18 +253,6 @@ class ExternalViewEmbedder {
   // This is called after submitting the embedder frame and the surface frame.
   virtual void FinishFrame();
 
-  // This should only be called after |SubmitFrame|.
-  // This method provides the embedder a way to do additional tasks after
-  // |SubmitFrame|. After invoking this method, the current task on the
-  // TaskRunner should end immediately.
-  //
-  // For example on the iOS embedder, threads are merged in this call.
-  // A new frame on the platform thread starts immediately. If the GPU thread
-  // still has some task running, there could be two frames being rendered
-  // concurrently, which causes undefined behaviors.
-  virtual void EndFrame(
-      fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {}
-
   FML_DISALLOW_COPY_AND_ASSIGN(ExternalViewEmbedder);
 
 };  // ExternalViewEmbedder

shell/common/BUILD.gn

@@ -191,8 +191,6 @@ if (enable_unittests) {
       "pipeline_unittests.cc",
       "shell_test.cc",
       "shell_test.h",
-      "shell_test_external_view_embedder.cc",
-      "shell_test_external_view_embedder.h",
       "shell_test_platform_view.cc",
       "shell_test_platform_view.h",
       "shell_unittests.cc",

shell/common/animator_unittests.cc

@@ -55,7 +55,7 @@ TEST_F(ShellTest, VSyncTargetTime) {
           return ShellTestPlatformView::Create(
               shell, shell.GetTaskRunners(), vsync_clock,
               std::move(create_vsync_waiter),
-              ShellTestPlatformView::BackendType::kDefaultBackend, nullptr);
+              ShellTestPlatformView::BackendType::kDefaultBackend);
         },
         [](Shell& shell) {
           return std::make_unique<Rasterizer>(shell, shell.GetTaskRunners());

shell/common/rasterizer.cc

@@ -136,16 +136,6 @@ void Rasterizer::Draw(fml::RefPtr<Pipeline<flutter::LayerTree>> pipeline) {
     consume_result = PipelineConsumeResult::MoreAvailable;
   }
 
-  // Merging the thread as we know the next `Draw` should be run on the platform
-  // thread.
-  if (raster_status == RasterStatus::kResubmit) {
-    auto* external_view_embedder = surface_->GetExternalViewEmbedder();
-    // We know only the `external_view_embedder` can
-    // causes|RasterStatus::kResubmit|. Check to make sure.
-    FML_DCHECK(external_view_embedder != nullptr);
-    external_view_embedder->EndFrame(raster_thread_merger_);
-  }
-
   // Consume as many pipeline items as possible. But yield the event loop
   // between successive tries.
   switch (consume_result) {

shell/common/shell_test.cc

@@ -260,12 +260,9 @@ std::unique_ptr<Shell> ShellTest::CreateShell(Settings settings,
                      simulate_vsync);
 }
 
-std::unique_ptr<Shell> ShellTest::CreateShell(
-    Settings settings,
-    TaskRunners task_runners,
-    bool simulate_vsync,
-    std::shared_ptr<ShellTestExternalViewEmbedder>
-        shell_test_external_view_embedder) {
+std::unique_ptr<Shell> ShellTest::CreateShell(Settings settings,
+                                              TaskRunners task_runners,
+                                              bool simulate_vsync) {
   const auto vsync_clock = std::make_shared<ShellTestVsyncClock>();
   CreateVsyncWaiter create_vsync_waiter = [&]() {
     if (simulate_vsync) {
@@ -278,18 +275,17 @@ std::unique_ptr<Shell> ShellTest::CreateShell(
   };
   return Shell::Create(
       task_runners, settings,
-      [vsync_clock, &create_vsync_waiter,
-       shell_test_external_view_embedder](Shell& shell) {
+      [vsync_clock, &create_vsync_waiter](Shell& shell) {
         return ShellTestPlatformView::Create(
             shell, shell.GetTaskRunners(), vsync_clock,
             std::move(create_vsync_waiter),
-            ShellTestPlatformView::BackendType::kDefaultBackend,
-            shell_test_external_view_embedder);
+            ShellTestPlatformView::BackendType::kDefaultBackend);
       },
       [](Shell& shell) {
         return std::make_unique<Rasterizer>(shell, shell.GetTaskRunners());
       });
 }
+
 void ShellTest::DestroyShell(std::unique_ptr<Shell> shell) {
   DestroyShell(std::move(shell), GetTaskRunnersForFixture());
 }

shell/common/shell_test.h

@@ -15,7 +15,6 @@
 #include "flutter/lib/ui/window/platform_message.h"
 #include "flutter/shell/common/run_configuration.h"
 #include "flutter/shell/common/shell.h"
-#include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/thread_host.h"
 #include "flutter/shell/common/vsync_waiters_test.h"
 #include "flutter/testing/elf_loader.h"
@@ -32,12 +31,9 @@ class ShellTest : public ThreadTest {
   Settings CreateSettingsForFixture();
   std::unique_ptr<Shell> CreateShell(Settings settings,
                                      bool simulate_vsync = false);
-  std::unique_ptr<Shell> CreateShell(
-      Settings settings,
-      TaskRunners task_runners,
-      bool simulate_vsync = false,
-      std::shared_ptr<ShellTestExternalViewEmbedder>
-          shell_test_external_view_embedder = nullptr);
+  std::unique_ptr<Shell> CreateShell(Settings settings,
+                                     TaskRunners task_runners,
+                                     bool simulate_vsync = false);
   void DestroyShell(std::unique_ptr<Shell> shell);
   void DestroyShell(std::unique_ptr<Shell> shell, TaskRunners task_runners);
   TaskRunners GetTaskRunnersForFixture();

shell/common/shell_test_external_view_embedder.cc

-#include "shell_test_external_view_embedder.h"
-
-namespace flutter {
-
-// |ExternalViewEmbedder|
-void ShellTestExternalViewEmbedder::CancelFrame() {}
-
-// |ExternalViewEmbedder|
-void ShellTestExternalViewEmbedder::BeginFrame(SkISize frame_size,
-                                               GrContext* context,
-                                               double device_pixel_ratio) {}
-
-// |ExternalViewEmbedder|
-void ShellTestExternalViewEmbedder::PrerollCompositeEmbeddedView(
-    int view_id,
-    std::unique_ptr<EmbeddedViewParams> params) {}
-
-// |ExternalViewEmbedder|
-PostPrerollResult ShellTestExternalViewEmbedder::PostPrerollAction(
-    fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {
-  FML_DCHECK(raster_thread_merger);
-  return post_preroll_result_;
-}
-
-// |ExternalViewEmbedder|
-std::vector<SkCanvas*> ShellTestExternalViewEmbedder::GetCurrentCanvases() {
-  return {};
-}
-
-// |ExternalViewEmbedder|
-SkCanvas* ShellTestExternalViewEmbedder::CompositeEmbeddedView(int view_id) {
-  return nullptr;
-}
-
-// |ExternalViewEmbedder|
-bool ShellTestExternalViewEmbedder::SubmitFrame(GrContext* context,
-                                                SkCanvas* background_canvas) {
-  return true;
-}
-
-// |ExternalViewEmbedder|
-void ShellTestExternalViewEmbedder::FinishFrame() {}
-
-// |ExternalViewEmbedder|
-void ShellTestExternalViewEmbedder::EndFrame(
-    fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {
-  end_frame_call_back_();
-}
-
-// |ExternalViewEmbedder|
-SkCanvas* ShellTestExternalViewEmbedder::GetRootCanvas() {
-  return nullptr;
-}
-
-}  // namespace flutter

shell/common/shell_test_external_view_embedder.h

-// Copyright 2013 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef FLUTTER_SHELL_TEST_EXTERNAL_VIEW_EMBEDDER_H_
-#define FLUTTER_SHELL_TEST_EXTERNAL_VIEW_EMBEDDER_H_
-
-#include "flutter/flow/embedded_views.h"
-#include "flutter/fml/raster_thread_merger.h"
-
-namespace flutter {
-
-//------------------------------------------------------------------------------
-/// @brief The external view embedder used by |ShellTestPlatformViewGL|
-///
-class ShellTestExternalViewEmbedder final : public ExternalViewEmbedder {
- public:
-  using EndFrameCallBack = std::function<void(void)>;
-
-  ShellTestExternalViewEmbedder(const EndFrameCallBack& end_frame_call_back,
-                                PostPrerollResult post_preroll_result)
-      : end_frame_call_back_(end_frame_call_back),
-        post_preroll_result_(post_preroll_result) {}
-
-  ~ShellTestExternalViewEmbedder() = default;
-
- private:
-  // |ExternalViewEmbedder|
-  void CancelFrame() override;
-
-  // |ExternalViewEmbedder|
-  void BeginFrame(SkISize frame_size,
-                  GrContext* context,
-                  double device_pixel_ratio) override;
-
-  // |ExternalViewEmbedder|
-  void PrerollCompositeEmbeddedView(
-      int view_id,
-      std::unique_ptr<EmbeddedViewParams> params) override;
-
-  // |ExternalViewEmbedder|
-  PostPrerollResult PostPrerollAction(
-      fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) override;
-
-  // |ExternalViewEmbedder|
-  std::vector<SkCanvas*> GetCurrentCanvases() override;
-
-  // |ExternalViewEmbedder|
-  SkCanvas* CompositeEmbeddedView(int view_id) override;
-
-  // |ExternalViewEmbedder|
-  bool SubmitFrame(GrContext* context, SkCanvas* background_canvas) override;
-
-  // |ExternalViewEmbedder|
-  void FinishFrame() override;
-
-  // |ExternalViewEmbedder|
-  void EndFrame(
-      fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) override;
-
-  // |ExternalViewEmbedder|
-  SkCanvas* GetRootCanvas() override;
-
-  const EndFrameCallBack end_frame_call_back_;
-  const PostPrerollResult post_preroll_result_;
-
-  FML_DISALLOW_COPY_AND_ASSIGN(ShellTestExternalViewEmbedder);
-};
-
-}  // namespace flutter
-
-#endif  // FLUTTER_SHELL_TEST_EXTERNAL_VIEW_EMBEDDER_H_

shell/common/shell_test_platform_view.cc

@@ -19,9 +19,7 @@ std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::Create(
     TaskRunners task_runners,
     std::shared_ptr<ShellTestVsyncClock> vsync_clock,
     CreateVsyncWaiter create_vsync_waiter,
-    BackendType backend,
-    std::shared_ptr<ShellTestExternalViewEmbedder>
-        shell_test_external_view_embedder) {
+    BackendType backend) {
   // TODO(gw280): https://github.com/flutter/flutter/issues/50298
   // Make this fully runtime configurable
   switch (backend) {
@@ -29,14 +27,12 @@ std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::Create(
 #ifdef SHELL_ENABLE_GL
     case BackendType::kGLBackend:
       return std::make_unique<ShellTestPlatformViewGL>(
-          delegate, task_runners, vsync_clock, create_vsync_waiter,
-          shell_test_external_view_embedder);
+          delegate, task_runners, vsync_clock, create_vsync_waiter);
 #endif  // SHELL_ENABLE_GL
 #ifdef SHELL_ENABLE_VULKAN
     case BackendType::kVulkanBackend:
       return std::make_unique<ShellTestPlatformViewVulkan>(
-          delegate, task_runners, vsync_clock, create_vsync_waiter,
-          shell_test_external_view_embedder);
+          delegate, task_runners, vsync_clock, create_vsync_waiter);
 #endif  // SHELL_ENABLE_VULKAN
     default:
       FML_LOG(FATAL) << "No backends supported for ShellTestPlatformView";

shell/common/shell_test_platform_view.h

@@ -6,7 +6,6 @@
 #define FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_H_
 
 #include "flutter/shell/common/platform_view.h"
-#include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/vsync_waiters_test.h"
 
 namespace flutter {
@@ -25,9 +24,7 @@ class ShellTestPlatformView : public PlatformView {
       TaskRunners task_runners,
       std::shared_ptr<ShellTestVsyncClock> vsync_clock,
       CreateVsyncWaiter create_vsync_waiter,
-      BackendType backend,
-      std::shared_ptr<ShellTestExternalViewEmbedder>
-          shell_test_external_view_embedder);
+      BackendType backend);
 
   virtual void SimulateVSync() = 0;
 

shell/common/shell_test_platform_view_gl.cc

@@ -12,14 +12,11 @@ ShellTestPlatformViewGL::ShellTestPlatformViewGL(
     PlatformView::Delegate& delegate,
     TaskRunners task_runners,
     std::shared_ptr<ShellTestVsyncClock> vsync_clock,
-    CreateVsyncWaiter create_vsync_waiter,
-    std::shared_ptr<ShellTestExternalViewEmbedder>
-        shell_test_external_view_embedder)
+    CreateVsyncWaiter create_vsync_waiter)
     : ShellTestPlatformView(delegate, std::move(task_runners)),
       gl_surface_(SkISize::Make(800, 600)),
       create_vsync_waiter_(std::move(create_vsync_waiter)),
-      vsync_clock_(vsync_clock),
-      shell_test_external_view_embedder_(shell_test_external_view_embedder) {}
+      vsync_clock_(vsync_clock) {}
 
 ShellTestPlatformViewGL::~ShellTestPlatformViewGL() = default;
 
@@ -73,7 +70,7 @@ ShellTestPlatformViewGL::GetGLProcResolver() const {
 
 // |GPUSurfaceGLDelegate|
 ExternalViewEmbedder* ShellTestPlatformViewGL::GetExternalViewEmbedder() {
-  return shell_test_external_view_embedder_.get();
+  return nullptr;
 }
 
 }  // namespace testing

shell/common/shell_test_platform_view_gl.h

@@ -5,7 +5,6 @@
 #ifndef FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_GL_H_
 #define FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_GL_H_
 
-#include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/shell_test_platform_view.h"
 #include "flutter/shell/gpu/gpu_surface_gl_delegate.h"
 #include "flutter/testing/test_gl_surface.h"
@@ -19,9 +18,7 @@ class ShellTestPlatformViewGL : public ShellTestPlatformView,
   ShellTestPlatformViewGL(PlatformView::Delegate& delegate,
                           TaskRunners task_runners,
                           std::shared_ptr<ShellTestVsyncClock> vsync_clock,
-                          CreateVsyncWaiter create_vsync_waiter,
-                          std::shared_ptr<ShellTestExternalViewEmbedder>
-                              shell_test_external_view_embedder);
+                          CreateVsyncWaiter create_vsync_waiter);
 
   virtual ~ShellTestPlatformViewGL() override;
 
@@ -34,9 +31,6 @@ class ShellTestPlatformViewGL : public ShellTestPlatformView,
 
   std::shared_ptr<ShellTestVsyncClock> vsync_clock_;
 
-  std::shared_ptr<ShellTestExternalViewEmbedder>
-      shell_test_external_view_embedder_;
-
   // |PlatformView|
   std::unique_ptr<Surface> CreateRenderingSurface() override;
 

shell/common/shell_test_platform_view_vulkan.cc

@@ -11,14 +11,11 @@ ShellTestPlatformViewVulkan::ShellTestPlatformViewVulkan(
     PlatformView::Delegate& delegate,
     TaskRunners task_runners,
     std::shared_ptr<ShellTestVsyncClock> vsync_clock,
-    CreateVsyncWaiter create_vsync_waiter,
-    std::shared_ptr<ShellTestExternalViewEmbedder>
-        shell_test_external_view_embedder)
+    CreateVsyncWaiter create_vsync_waiter)
     : ShellTestPlatformView(delegate, std::move(task_runners)),
       create_vsync_waiter_(std::move(create_vsync_waiter)),
       vsync_clock_(vsync_clock),
-      proc_table_(fml::MakeRefCounted<vulkan::VulkanProcTable>()),
-      shell_test_external_view_embedder_(shell_test_external_view_embedder) {}
+      proc_table_(fml::MakeRefCounted<vulkan::VulkanProcTable>()) {}
 
 ShellTestPlatformViewVulkan::~ShellTestPlatformViewVulkan() = default;
 
@@ -32,8 +29,7 @@ void ShellTestPlatformViewVulkan::SimulateVSync() {
 
 // |PlatformView|
 std::unique_ptr<Surface> ShellTestPlatformViewVulkan::CreateRenderingSurface() {
-  return std::make_unique<OffScreenSurface>(proc_table_,
-                                            shell_test_external_view_embedder_);
+  return std::make_unique<OffScreenSurface>(proc_table_);
 }
 
 // |PlatformView|
@@ -48,12 +44,8 @@ PointerDataDispatcherMaker ShellTestPlatformViewVulkan::GetDispatcherMaker() {
 //              We need to merge this functionality back into //vulkan.
 //              https://github.com/flutter/flutter/issues/51132
 ShellTestPlatformViewVulkan::OffScreenSurface::OffScreenSurface(
-    fml::RefPtr<vulkan::VulkanProcTable> vk,
-    std::shared_ptr<ShellTestExternalViewEmbedder>
-        shell_test_external_view_embedder)
-    : valid_(false),
-      vk_(std::move(vk)),
-      shell_test_external_view_embedder_(shell_test_external_view_embedder) {
+    fml::RefPtr<vulkan::VulkanProcTable> vk)
+    : valid_(false), vk_(std::move(vk)) {
   if (!vk_ || !vk_->HasAcquiredMandatoryProcAddresses()) {
     FML_DLOG(ERROR) << "Proc table has not acquired mandatory proc addresses.";
     return;
@@ -178,10 +170,5 @@ SkMatrix ShellTestPlatformViewVulkan::OffScreenSurface::GetRootTransformation()
   return matrix;
 }
 
-flutter::ExternalViewEmbedder*
-ShellTestPlatformViewVulkan::OffScreenSurface::GetExternalViewEmbedder() {
-  return shell_test_external_view_embedder_.get();
-}
-
 }  // namespace testing
 }  // namespace flutter

shell/common/shell_test_platform_view_vulkan.h

@@ -5,7 +5,6 @@
 #ifndef FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_VULKAN_H_
 #define FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_VULKAN_H_
 
-#include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/shell_test_platform_view.h"
 #include "flutter/shell/gpu/gpu_surface_vulkan_delegate.h"
 #include "flutter/vulkan/vulkan_application.h"
@@ -19,9 +18,7 @@ class ShellTestPlatformViewVulkan : public ShellTestPlatformView {
   ShellTestPlatformViewVulkan(PlatformView::Delegate& delegate,
                               TaskRunners task_runners,
                               std::shared_ptr<ShellTestVsyncClock> vsync_clock,
-                              CreateVsyncWaiter create_vsync_waiter,
-                              std::shared_ptr<ShellTestExternalViewEmbedder>
-                                  shell_test_external_view_embedder);
+                              CreateVsyncWaiter create_vsync_waiter);
 
   ~ShellTestPlatformViewVulkan() override;
 
@@ -30,9 +27,7 @@ class ShellTestPlatformViewVulkan : public ShellTestPlatformView {
  private:
   class OffScreenSurface : public flutter::Surface {
    public:
-    OffScreenSurface(fml::RefPtr<vulkan::VulkanProcTable> vk,
-                     std::shared_ptr<ShellTestExternalViewEmbedder>
-                         shell_test_external_view_embedder);
+    OffScreenSurface(fml::RefPtr<vulkan::VulkanProcTable> vk);
 
     ~OffScreenSurface() override;
 
@@ -47,13 +42,9 @@ class ShellTestPlatformViewVulkan : public ShellTestPlatformView {
     // |Surface|
     GrContext* GetContext() override;
 
-    flutter::ExternalViewEmbedder* GetExternalViewEmbedder() override;
-
    private:
     bool valid_;
     fml::RefPtr<vulkan::VulkanProcTable> vk_;
-    std::shared_ptr<ShellTestExternalViewEmbedder>
-        shell_test_external_view_embedder_;
     std::unique_ptr<vulkan::VulkanApplication> application_;
     std::unique_ptr<vulkan::VulkanDevice> logical_device_;
     sk_sp<GrContext> context_;
@@ -70,9 +61,6 @@ class ShellTestPlatformViewVulkan : public ShellTestPlatformView {
 
   fml::RefPtr<vulkan::VulkanProcTable> proc_table_;
 
-  std::shared_ptr<ShellTestExternalViewEmbedder>
-      shell_test_external_view_embedder_;
-
   // |PlatformView|
   std::unique_ptr<Surface> CreateRenderingSurface() override;
 

shell/common/shell_unittests.cc

@@ -23,7 +23,6 @@
 #include "flutter/shell/common/platform_view.h"
 #include "flutter/shell/common/rasterizer.h"
 #include "flutter/shell/common/shell_test.h"
-#include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/shell_test_platform_view.h"
 #include "flutter/shell/common/switches.h"
 #include "flutter/shell/common/thread_host.h"
@@ -140,7 +139,7 @@ TEST_F(ShellTest,
               return static_cast<std::unique_ptr<VsyncWaiter>>(
                   std::make_unique<VsyncWaiterFallback>(task_runners));
             },
-            ShellTestPlatformView::BackendType::kDefaultBackend, nullptr);
+            ShellTestPlatformView::BackendType::kDefaultBackend);
       },
       [](Shell& shell) {
         return std::make_unique<Rasterizer>(shell, shell.GetTaskRunners());
@@ -467,51 +466,6 @@ TEST_F(ShellTest, FrameRasterizedCallbackIsCalled) {
   DestroyShell(std::move(shell));
 }
 
-TEST_F(ShellTest,
-       ExternalEmbedderEndFrameIsCalledWhenPostPrerollResultIsResubmit) {
-  auto settings = CreateSettingsForFixture();
-  fml::AutoResetWaitableEvent endFrameLatch;
-  bool end_frame_called = false;
-  auto end_frame_callback = [&] {
-    end_frame_called = true;
-    endFrameLatch.Signal();
-  };
-  auto external_view_embedder = std::make_shared<ShellTestExternalViewEmbedder>(
-      end_frame_callback, PostPrerollResult::kResubmitFrame);
-  auto shell = CreateShell(std::move(settings), GetTaskRunnersForFixture(),
-                           false, external_view_embedder);
-
-  // Create the surface needed by rasterizer
-  PlatformViewNotifyCreated(shell.get());
-
-  auto configuration = RunConfiguration::InferFromSettings(settings);
-  configuration.SetEntrypoint("emptyMain");
-
-  RunEngine(shell.get(), std::move(configuration));
-
-  LayerTreeBuilder builder = [&](std::shared_ptr<ContainerLayer> root) {
-    SkPictureRecorder recorder;
-    SkCanvas* recording_canvas =
-        recorder.beginRecording(SkRect::MakeXYWH(0, 0, 80, 80));
-    recording_canvas->drawRect(SkRect::MakeXYWH(0, 0, 80, 80),
-                               SkPaint(SkColor4f::FromColor(SK_ColorRED)));
-    auto sk_picture = recorder.finishRecordingAsPicture();
-    fml::RefPtr<SkiaUnrefQueue> queue = fml::MakeRefCounted<SkiaUnrefQueue>(
-        this->GetCurrentTaskRunner(), fml::TimeDelta::FromSeconds(0));
-    auto picture_layer = std::make_shared<PictureLayer>(
-        SkPoint::Make(10, 10),
-        flutter::SkiaGPUObject<SkPicture>({sk_picture, queue}), false, false);
-    root->Add(picture_layer);
-  };
-
-  PumpOneFrame(shell.get(), 100, 100, builder);
-  endFrameLatch.Wait();
-
-  ASSERT_TRUE(end_frame_called);
-
-  DestroyShell(std::move(shell));
-}
-
 TEST(SettingsTest, FrameTimingSetsAndGetsProperly) {
   // Ensure that all phases are in kPhases.
   ASSERT_EQ(sizeof(FrameTiming::kPhases),

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm

@@ -248,7 +248,7 @@ void FlutterPlatformViewsController::SetFrameSize(SkISize frame_size) {
 }
 
 void FlutterPlatformViewsController::CancelFrame() {
-  composition_order_ = active_composition_order_;
+  composition_order_.clear();
 }
 
 bool FlutterPlatformViewsController::HasPendingViewOperations() {
@@ -267,9 +267,8 @@ PostPrerollResult FlutterPlatformViewsController::PostPrerollAction(
     if (raster_thread_merger->IsMerged()) {
       raster_thread_merger->ExtendLeaseTo(kDefaultMergedLeaseDuration);
     } else {
-      // Wait until |EndFrame| to merge the threads.
-      merge_threads_ = true;
       CancelFrame();
+      raster_thread_merger->MergeWithLease(kDefaultMergedLeaseDuration);
       return PostPrerollResult::kResubmitFrame;
     }
   }
@@ -469,21 +468,6 @@ SkRect FlutterPlatformViewsController::GetPlatformViewRect(int view_id) {
 bool FlutterPlatformViewsController::SubmitFrame(GrContext* gr_context,
                                                  std::shared_ptr<IOSContext> ios_context,
                                                  SkCanvas* background_canvas) {
-  if (merge_threads_) {
-    // Threads are about to be merged, we drop everything from this frame
-    // and possibly resubmit the same layer tree in the next frame.
-    // Before merging thread, we know the code is not running on the main thread. Assert that
-    FML_DCHECK(![[NSThread currentThread] isMainThread]);
-    picture_recorders_.clear();
-    composition_order_.clear();
-    return true;
-  }
-
-  // Any UIKit related code has to run on main thread.
-  // When on a non-main thread, we only allow the rest of the method to run if there is no platform
-  // view.
-  FML_DCHECK([[NSThread currentThread] isMainThread] || views_to_dispose_.empty());
-
   DisposeViews();
 
   // Resolve all pending GPU operations before allocating a new surface.
@@ -594,14 +578,6 @@ void FlutterPlatformViewsController::BringLayersIntoView(LayersMap layer_map) {
   }
 }
 
-void FlutterPlatformViewsController::EndFrame(
-    fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {
-  if (merge_threads_) {
-    raster_thread_merger->MergeWithLease(kDefaultMergedLeaseDuration);
-    merge_threads_ = false;
-  }
-}
-
 std::shared_ptr<FlutterPlatformViewLayer> FlutterPlatformViewsController::GetLayer(
     GrContext* gr_context,
     std::shared_ptr<IOSContext> ios_context,
@@ -666,8 +642,6 @@ void FlutterPlatformViewsController::DisposeViews() {
     return;
   }
 
-  FML_DCHECK([[NSThread currentThread] isMainThread]);
-
   for (int64_t viewId : views_to_dispose_) {
     UIView* root_view = root_views_[viewId].get();
     [root_view removeFromSuperview];

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h

@@ -134,8 +134,6 @@ class FlutterPlatformViewsController {
 
   void SetFrameSize(SkISize frame_size);
 
-  // Indicates that we don't compisite any platform views or overlays during this frame.
-  // Also reverts the composition_order_ to its original state at the begining of the frame.
   void CancelFrame();
 
   void PrerollCompositeEmbeddedView(int view_id,
@@ -165,11 +163,6 @@ class FlutterPlatformViewsController {
                    std::shared_ptr<IOSContext> ios_context,
                    SkCanvas* background_canvas);
 
-  // Invoked at the very end of a frame.
-  // After invoking this method, nothing should happen on the current TaskRunner during the same
-  // frame.
-  void EndFrame(fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger);
-
   void OnMethodCall(FlutterMethodCall* call, FlutterResult& result);
 
  private:
@@ -280,10 +273,6 @@ class FlutterPlatformViewsController {
   void ApplyMutators(const MutatorsStack& mutators_stack, UIView* embedded_view);
   void CompositeWithParams(int view_id, const EmbeddedViewParams& params);
 
-  // Default to `false`.
-  // If `true`, gpu thread and platform thread should be merged during |EndFrame|.
-  // Always resets to `false` right after the threads are merged.
-  bool merge_threads_;
   // Allocates a new FlutterPlatformViewLayer if needed, draws the pixels within the rect from
   // the picture on the layer's canvas.
   std::shared_ptr<FlutterPlatformViewLayer> GetLayer(GrContext* gr_context,
@@ -293,7 +282,6 @@ class FlutterPlatformViewsController {
                                                      int64_t view_id,
                                                      int64_t overlay_id);
   // Removes overlay views and platform views that aren't needed in the current frame.
-  // Must run on the platform thread.
   void RemoveUnusedLayers();
   // Appends the overlay views and platform view and sets their z index based on the composition
   // order.

shell/platform/darwin/ios/ios_surface.h

@@ -83,9 +83,6 @@ class IOSSurface : public ExternalViewEmbedder {
   // |ExternalViewEmbedder|
   void FinishFrame() override;
 
-  // |ExternalViewEmbedder|
-  void EndFrame(fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) override;
-
  public:
   FML_DISALLOW_COPY_AND_ASSIGN(IOSSurface);
 };

shell/platform/darwin/ios/ios_surface.mm

@@ -90,12 +90,7 @@ void IOSSurface::CancelFrame() {
   platform_views_controller_->CancelFrame();
   // Committing the current transaction as |BeginFrame| will create a nested
   // CATransaction otherwise.
-  if ([[NSThread currentThread] isMainThread]) {
-    // The only time we need to commit the `CATranscation` is when
-    // there are platform views in the scene, which has to be run on the
-    // main thread.
-    [CATransaction commit];
-  }
+  [CATransaction commit];
 }
 
 // |ExternalViewEmbedder|
@@ -103,12 +98,7 @@ void IOSSurface::BeginFrame(SkISize frame_size, GrContext* context, double devic
   TRACE_EVENT0("flutter", "IOSSurface::BeginFrame");
   FML_CHECK(platform_views_controller_ != nullptr);
   platform_views_controller_->SetFrameSize(frame_size);
-  if ([[NSThread currentThread] isMainThread]) {
-    // The only time we need to commit the `CATranscation` is when
-    // there are platform views in the scene, which has to be run on the
-    // main thread.
-    [CATransaction begin];
-  }
+  [CATransaction begin];
 }
 
 // |ExternalViewEmbedder|
@@ -150,22 +140,10 @@ bool IOSSurface::SubmitFrame(GrContext* context, SkCanvas* background_canvas) {
   return submitted;
 }
 
-// |ExternalViewEmbedder|
-void IOSSurface::EndFrame(fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {
-  TRACE_EVENT0("flutter", "IOSSurface::EndFrame");
-  FML_CHECK(platform_views_controller_ != nullptr);
-  return platform_views_controller_->EndFrame(raster_thread_merger);
-}
-
 // |ExternalViewEmbedder|
 void IOSSurface::FinishFrame() {
   TRACE_EVENT0("flutter", "IOSSurface::DidSubmitFrame");
-  if (![[NSThread currentThread] isMainThread]) {
-    return;
-  }
-  // The only time we need to commit the `CATranscation` is when
-  // there are platform views in the scene, which has to be run on the
-  // main thread.
   [CATransaction commit];
 }
+
 }  // namespace flutter