Switch to using precompiled snapshots on iOS

DEPS

@@ -25,7 +25,7 @@ vars = {
 
   # Note: When updating the Dart revision, ensure that all entries that are
   # dependencies of dart are also updated
-  'dart_revision': '6aab1cecb25f8e04087320f2082336073628afb4',
+  'dart_revision': '2da9b9ce0a786c9dc7742a1045ed5b326c73076d',
   'dart_observatory_packages_revision': '5c199c5954146747f75ed127871207718dc87786',
   'dart_root_certificates_revision': 'c3a41df63afacec62fcb8135196177e35fe72f71',
 

build/config/compiler/BUILD.gn

@@ -67,7 +67,7 @@ declare_args() {
   # depending on the application type, may be unnecessary. If the type of
   # architecture is known beforehand, setting that as the active arch will
   # greatly reduce build times and reduce binary sizes.
-  ios_active_arch = "armv7"
+  ios_active_arch = "arm64"
 }
 
 # default_include_dirs ---------------------------------------------------------

sky/BUILD.gn

@@ -10,7 +10,6 @@ group("sky") {
     "//sky/engine/wtf:unittests($host_toolchain)",
     "//examples",
     "//sky/tools/imagediff($host_toolchain)",
-    "//sky/tools/sky_snapshot($host_toolchain)",
     ":sky_dev",
   ]
 

sky/build/flx.gni

@@ -36,6 +36,11 @@ template("flx") {
       "--output-file", rebase_path(bundle, root_build_dir),
     ]
 
+    if(is_ios) {
+      # This makes the tools bypass the script snapshot compiler
+      args += [ "--precompiled" ]
+    }
+
     if (defined(invoker.manifest)) {
       inputs += [ invoker.manifest ]
       args += [

sky/build/sky_app.gni

@@ -95,6 +95,7 @@ template("sky_app") {
   } else if (is_ios && defined(invoker.info_plist)) {
     import("//build/config/ios/rules.gni")
     import("//build/config/ios/ios_sdk.gni")
+    import("//sky/engine/bindings/bindings.gni")
 
     ios_app(target_name) {
       app_name = target_name + "_app"
@@ -124,10 +125,17 @@ template("sky_app") {
         deps = [ ":app" ]
       }
 
+      precompiled_gen_target = target_name + "_precompiled"
+      dart_precompile(precompiled_gen_target) {
+        dart_package_root = rebase_path("packages", root_build_dir)
+        dart_script = invoker.main_dart
+      }
+
       deps = [
         "//sky/shell:ios_scaffolding",
         ":$resources_gen_target_name",
         ":$flx_target_name",
+        ":$precompiled_gen_target",
       ]
 
       if (defined(invoker.deps)) {

sky/dist/BUILD.gn

@@ -27,7 +27,7 @@ copy("sky_shell") {
     deps = [
       "//sky/shell",
     ]
-  } else if (is_ios || is_mac) {
+  } else if (is_mac) {
     sources = [
       "$root_build_dir/SkyShell.app",
     ]
@@ -35,7 +35,7 @@ copy("sky_shell") {
     deps = [
       "//sky/shell:shell_struct",
     ]
-  } else {
+  } else if(!is_ios) {
     sources = [
       "$root_build_dir/sky_shell",
       "$root_build_dir/icudtl.dat",
@@ -45,6 +45,9 @@ copy("sky_shell") {
       "//sky/shell",
       "//third_party/icu:icudata",
     ]
+  } else {
+    sources = []
+    deps = []
   }
 
   sky_snapshot_dir =

sky/engine/bindings/BUILD.gn

@@ -41,9 +41,18 @@ source_set("bindings") {
     "//sky/engine/tonic",
     "//sky/engine/wtf",
     ":generated_bindings",
-    ":snapshot_cc",
-    ":updater_snapshot_cc",
   ]
+
+  # On iOS, precompiled snapshots contain the instruction buffer. Generation
+  # of the same requires all application specific script code to be specified
+  # up front. In such cases, there can be no updater or generic snapshotter
+  if (!is_ios) {
+    deps += [
+      ":snapshot_cc",
+      ":updater_snapshot_cc",
+    ]
+  }
+
   include_dirs = [
     "..",
     "$root_build_dir",

sky/engine/bindings/bindings.gni

@@ -48,3 +48,118 @@ idl_compiler_files = [
   "scripts/v8_types.py",
   "scripts/v8_utilities.py",
 ]
+
+template("dart_precompile") {
+  assert(defined(invoker.dart_package_root),
+         "The dart package root must be defined")
+  assert(defined(invoker.dart_script),
+         "The dart script must be specified")
+
+  vm_isolate_snapshot_name = target_name + "_vm_isolate.bin"
+  vm_isolate_snapshot = "$target_gen_dir/$vm_isolate_snapshot_name"
+  isolate_snapshot_name = target_name + "_isolate.bin"
+  isolate_snapshot = "$target_gen_dir/$isolate_snapshot_name"
+  
+  assembly_path =
+      "$target_gen_dir/" + target_name + "_instructions.S"
+  instructions_gen_target_name = target_name + "_instructions"
+  action(instructions_gen_target_name) {
+    deps = [
+      "//dart/runtime/bin:gen_snapshot($host_toolchain)",
+    ]
+    embedder_entry_points_manifest =
+        "//sky/engine/bindings/dart_vm_entry_points.txt"
+    inputs = [
+      "//dart/runtime/tools/create_snapshot_bin.py",
+      "//mojo/public/dart/mojo/sdk_ext/internal.dart",
+      "//mojo/public/dart/mojo/sdk_ext/src/handle_watcher.dart",
+      "//mojo/public/dart/mojo/sdk_ext/src/natives.dart",
+      "//mojo/public/dart/mojo/sdk_ext/src/timer_queue.dart",
+      "//sky/engine/bindings/internals.dart",
+      embedder_entry_points_manifest,
+    ]
+    outputs = [
+      vm_isolate_snapshot,
+      isolate_snapshot,
+      assembly_path
+    ]
+
+    dart_mojo_internal_path =
+        rebase_path("//mojo/public/dart/mojo/sdk_ext/internal.dart")
+    dart_ui_internals_path =
+        rebase_path("//sky/engine/bindings/internals.dart")
+    dart_ui_path =
+        rebase_path("$root_build_dir/clang_x64/gen/sky/bindings/dart_ui.dart")
+
+    gen_snapshot_dir =
+        get_label_info("//dart/runtime/bin:gen_snapshot($host_toolchain)",
+                       "root_out_dir")
+    script = "//dart/runtime/tools/create_snapshot_bin.py"
+
+    args = [
+      "--executable",
+      rebase_path("$gen_snapshot_dir/gen_snapshot"),
+      "--package_root",
+      rebase_path(invoker.dart_package_root, root_build_dir),
+      "--script",
+      rebase_path(invoker.dart_script, root_build_dir),
+      "--vm_output_bin",
+      rebase_path(vm_isolate_snapshot, root_build_dir),
+      "--output_bin",
+      rebase_path(isolate_snapshot, root_build_dir),
+      "--instructions_bin",
+      rebase_path(assembly_path, root_build_dir),
+      "--embedder_entry_points_manifest",
+      rebase_path(embedder_entry_points_manifest, root_build_dir),
+      "--target_os",
+      target_os,
+      "--url_mapping=dart:mojo.internal,$dart_mojo_internal_path",
+      "--url_mapping=dart:ui,$dart_ui_path",
+      "--url_mapping=dart:ui_internals,$dart_ui_internals_path",
+    ]
+  }
+
+  snapshot_cc = "$target_gen_dir/" + target_name + "_precompiled_snapshot.cc"
+  snapshot_cc_gen_target_name = target_name + "_snapshot_cc"
+  action(snapshot_cc_gen_target_name) {
+    deps = [
+      ":$instructions_gen_target_name",
+    ]
+
+    template_file = "//sky/engine/bindings/snapshot.cc.tmpl"
+
+    inputs = [
+      template_file,
+      vm_isolate_snapshot,
+      isolate_snapshot,
+    ]
+
+    outputs = [
+      snapshot_cc,
+    ]
+
+    script = "//dart/runtime/tools/create_snapshot_file.py"
+    args = [
+      "--vm_input_bin",
+      rebase_path(vm_isolate_snapshot, root_build_dir),
+      "--input_bin",
+      rebase_path(isolate_snapshot, root_build_dir),
+      "--input_cc",
+      rebase_path(template_file, root_build_dir),
+      "--output",
+      rebase_path(snapshot_cc),
+    ]
+  }
+
+  source_set(target_name) {
+    sources = [
+      assembly_path,
+      snapshot_cc,
+    ]
+
+    deps = [
+      ":$instructions_gen_target_name",
+      ":$snapshot_cc_gen_target_name",
+    ]
+  }
+}

sky/engine/bindings/dart_natives.cc

@@ -118,9 +118,11 @@ static void InitDartInternal(Dart_Handle builtin_library,
   } else {
     CHECK(isolate_type == DartNatives::DartIOIsolate);
     Dart_Handle io_lib = DartBuiltin::LookupLibrary("dart:io");
+    DART_CHECK_VALID(io_lib);
     Dart_Handle setup_hooks = Dart_NewStringFromCString("_setupHooks");
     DART_CHECK_VALID(Dart_Invoke(io_lib, setup_hooks, 0, NULL));
     Dart_Handle isolate_lib = DartBuiltin::LookupLibrary("dart:isolate");
+    DART_CHECK_VALID(isolate_lib);
     DART_CHECK_VALID(Dart_Invoke(isolate_lib, setup_hooks, 0, NULL));
   }
 }

sky/engine/bindings/dart_vm_entry_points.txt

+dart:io,::,_setupHooks
+dart:mojo.internal,MojoHandleWatcher,_start
+dart:ui,::,_getCreateTimerClosure
+dart:ui,::,_getGetBaseURLClosure
+dart:ui,::,_getMainClosure
+dart:ui,::,_getPrintClosure
+dart:ui,::,_getScheduleMicrotaskClosure
+dart:ui,Canvas,Canvas.
+dart:ui,CharacterData,CharacterData.
+dart:ui,ClientRect,ClientRect.
+dart:ui,ClientRectList,ClientRectList.
+dart:ui,CSSStyleDeclaration,CSSStyleDeclaration.
+dart:ui,Document,Document.
+dart:ui,DocumentFragment,DocumentFragment.
+dart:ui,DOMError,DOMError.
+dart:ui,DOMException,DOMException.
+dart:ui,Drawable,Drawable.
+dart:ui,DrawLooper,DrawLooper.
+dart:ui,DrawLooperLayerInfo,DrawLooperLayerInfo.
+dart:ui,Element,Element.
+dart:ui,Event,Event.
+dart:ui,Event,Event.
+dart:ui,GestureVelocity,GestureVelocity.
+dart:ui,HTMLElement,HTMLElement.
+dart:ui,Image,Image.
+dart:ui,ImageData,ImageData.
+dart:ui,ImageShader,ImageShader.
+dart:ui,KeyboardEvent,KeyboardEvent.
+dart:ui,KeyboardEvent,KeyboardEvent.
+dart:ui,LayerDrawLooperBuilder,LayerDrawLooperBuilder.
+dart:ui,LayoutRoot,LayoutRoot.
+dart:ui,Node,Node.
+dart:ui,Paragraph,Paragraph.
+dart:ui,ParagraphBuilder,ParagraphBuilder.
+dart:ui,ParagraphStyle,ParagraphStyle.
+dart:ui,ParentNode,ParentNode.
+dart:ui,Path,Path.
+dart:ui,Picture,Picture.
+dart:ui,PictureRecorder,PictureRecorder.
+dart:ui,PointerEvent,PointerEvent.
+dart:ui,PointerEvent,PointerEvent.
+dart:ui,Range,Range.
+dart:ui,RRect,RRect.
+dart:ui,Scene,Scene.
+dart:ui,SceneBuilder,SceneBuilder.
+dart:ui,Shader,Shader.
+dart:ui,Text,Text.
+dart:ui,TextMetrics,TextMetrics.
+dart:ui,TextStyle,TextStyle.
+dart:ui,Tracing,Tracing.
+dart:ui,VelocityTracker,VelocityTracker.
+dart:ui,View,View.
+dart:ui,WheelEvent,WheelEvent.
+dart:ui,WheelEvent,WheelEvent.
+dart:ui_internals,::,takeRootBundleHandle
+dart:ui_internals,::,takeServiceRegistry
+dart:ui_internals,::,takeServicesProvidedByEmbedder
+dart:ui_internals,::,takeServicesProvidedToEmbedder
+dart:ui_internals,::,takeShellProxyHandle

sky/engine/bindings/snapshot.dart

@@ -10,7 +10,6 @@ import 'dart:io';
 import 'dart:isolate';
 import 'dart:math';
 import 'dart:mojo.internal';
-import 'dart:mirrors';
 import 'dart:ui';
 import 'dart:ui_internals';
 import 'dart:typed_data';

sky/engine/core/dart/natives.dart

@@ -53,3 +53,10 @@ _getPrintClosure() => _print;
 _getScheduleMicrotaskClosure() => _scheduleMicrotask;
 _getGetBaseURLClosure() =>_getBaseURL;
 _getCreateTimerClosure() => _createTimer;
+
+// Though the "main" symbol is not included in any of the libraries imported
+// above, the builtin library will be included manually during VM setup. This
+// symbol is only necessary for precompilation. It is marked as a stanalone
+// entry point into the VM. This prevents the precompiler from tree shaking
+// away "main"
+_getMainClosure() => main;

sky/engine/core/script/dart_controller.cc

@@ -95,11 +95,14 @@ void DartController::DidLoadSnapshot() {
   DartApiScope dart_api_scope;
 
   Dart_Handle library = Dart_RootLibrary();
-  if (LogIfError(library))
-    return;
+  DART_CHECK_VALID(library);
   DartInvokeAppField(library, ToDart("main"), 0, nullptr);
 }
 
+void DartController::RunFromPrecompiledSnapshot() {
+  DidLoadSnapshot();
+}
+
 void DartController::RunFromSnapshot(
     mojo::ScopedDataPipeConsumerHandle snapshot) {
   snapshot_loader_ = adoptPtr(new DartSnapshotLoader(dart_state()));

sky/engine/core/script/dart_controller.h

@@ -33,6 +33,7 @@ class DartController {
 
   void RunFromLibrary(const String& name,
                       DartLibraryProvider* library_provider);
+  void RunFromPrecompiledSnapshot();
   void RunFromSnapshot(mojo::ScopedDataPipeConsumerHandle snapshot);
   void RunFromSnapshotBuffer(const uint8_t* buffer, size_t size);
 

sky/engine/core/script/dart_init.cc

@@ -4,6 +4,8 @@
 
 #include "sky/engine/core/script/dart_init.h"
 
+#include <dlfcn.h>
+
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/single_thread_task_runner.h"
@@ -76,10 +78,16 @@ void CreateEmptyRootLibraryIfNeeded() {
 static const char* kDartArgs[] = {
     "--enable_mirrors=false",
 #if WTF_OS_IOS || WTF_OS_MACOSX
-    "--no-profile"
+    "--no-profile",
 #endif
 };
 
+static const char* kInstructionsSnapshotSymbolName = "kInstructionsSnapshot";
+
+static const char* kDartPrecompilationArgs[] {
+  "--precompilation",
+};
+
 static const char* kDartCheckedModeArgs[] = {
   "--enable_asserts",
   "--enable_type_checks",
@@ -100,6 +108,16 @@ bool IsServiceIsolateURL(const char* url_name) {
       String(url_name) == DART_VM_SERVICE_ISOLATE_NAME;
 }
 
+static const uint8_t* PrecompiledInstructionsSymbolIfPresent() {
+  dlerror();  // clear previous errors on thread
+  void * sym = dlsym(RTLD_SELF, kInstructionsSnapshotSymbolName);
+  return (dlerror() != nullptr) ? nullptr : reinterpret_cast<uint8_t * >(sym);
+}
+
+static bool IsRunningPrecompiledCode() {
+  return PrecompiledInstructionsSymbolIfPresent() != nullptr;
+}
+
 // TODO(rafaelw): Right now this only supports the creation of the handle
 // watcher isolate and the service isolate. Presumably, we'll want application
 // isolates to spawn their own isolates.
@@ -129,7 +147,8 @@ Dart_Isolate IsolateCreateCallback(const char* script_uri,
       // Start the handle watcher from the service isolate so it isn't available
       // for debugging or general Observatory interaction.
       EnsureHandleWatcherStarted();
-      if (RuntimeEnabledFeatures::observatoryEnabled()) {
+      if (!IsRunningPrecompiledCode() &&
+          RuntimeEnabledFeatures::observatoryEnabled()) {
         std::string ip = "127.0.0.1";
         const intptr_t port = 8181;
         const bool service_isolate_booted =
@@ -181,6 +200,10 @@ void InitDartVM() {
 
   Vector<const char*> args;
   args.append(kDartArgs, arraysize(kDartArgs));
+
+  if (IsRunningPrecompiledCode())
+    args.append(kDartPrecompilationArgs, arraysize(kDartPrecompilationArgs));
+
   if (enable_checked_mode)
     args.append(kDartCheckedModeArgs, arraysize(kDartCheckedModeArgs));
 
@@ -189,7 +212,7 @@ void InitDartVM() {
   DartDebugger::InitDebugger();
   CHECK(Dart_Initialize(
       kDartVmIsolateSnapshotBuffer,
-      nullptr,
+      PrecompiledInstructionsSymbolIfPresent(),
       IsolateCreateCallback,
       nullptr,  // Isolate interrupt callback.
       UnhandledExceptionCallback, IsolateShutdownCallback,

sky/engine/public/sky/sky_view.cc

@@ -59,6 +59,11 @@ void SkyView::RunFromLibrary(const WebString& name,
   dart_controller_->RunFromLibrary(name, library_provider);
 }
 
+void SkyView::RunFromPrecompiledSnapshot() {
+  DCHECK(view_);
+  dart_controller_->RunFromPrecompiledSnapshot();
+}
+
 void SkyView::RunFromSnapshot(const WebString& name,
                               mojo::ScopedDataPipeConsumerHandle snapshot) {
   DCHECK(view_);

sky/engine/public/sky/sky_view.h

@@ -42,6 +42,7 @@ class SkyView {
 
   void RunFromLibrary(const WebString& name,
                       DartLibraryProvider* library_provider);
+  void RunFromPrecompiledSnapshot();
   void RunFromSnapshot(const WebString& name,
                        mojo::ScopedDataPipeConsumerHandle snapshot);
 

sky/services/engine/sky_engine.mojom

@@ -27,6 +27,7 @@ interface SkyEngine {
 
   RunFromNetwork(string url);
   RunFromFile(string main, string package_root);
+  RunFromPrecompiledSnapshot();
   RunFromSnapshot(string path);
   RunFromBundle(string path);
 };

sky/shell/BUILD.gn

@@ -221,21 +221,9 @@ if (is_android) {
            ]
   }
 
-  ios_app("shell") {
-    app_name = "SkyShell"
-    info_plist = "ios/Info.plist"
-    entitlements_path = "ios/Entitlements.xcent"
-    code_signing_identity = ios_code_signing_identity
-
-    resource_copy_ios("sky_resources") {
-      resources = [ "//third_party/icu/android/icudtl.dat" ]
-      bundle_directory = "."
-    }
-
-    deps = [
-      ":ios_scaffolding",
-      ":sky_resources",
-    ]
+  group("shell") {
+    # iOS only supports application bundles with a precompiled instruction
+    # buffer. There is not Shell target for the same.
   }
 } else if (is_linux) {
   executable("shell") {

sky/shell/ios/sky_surface.mm

@@ -17,10 +17,6 @@
 #include "sky/shell/ui_delegate.h"
 #include <strings.h>
 
-#ifndef NDEBUG
-#include "document_watcher.h"
-#endif
-
 enum MapperPhase {
   Accessed,
   Added,
@@ -92,10 +88,6 @@ class TouchMapper {
   sky::SkyEnginePtr _sky_engine;
   scoped_ptr<sky::shell::ShellView> _shell_view;
   TouchMapper _touch_mapper;
-
-#ifndef NDEBUG
-  DocumentWatcher *_document_watcher;
-#endif
 }
 
 static std::string SkPictureTracingPath() {
@@ -104,7 +96,7 @@ static std::string SkPictureTracingPath() {
   return [paths.firstObject UTF8String];
 }
 
--(instancetype) initWithShellView:(sky::shell::ShellView *) shellView {
+- (instancetype)initWithShellView:(sky::shell::ShellView*)shellView {
   self = [super init];
   if (self) {
     base::FilePath pictureTracingPath =
@@ -140,7 +132,9 @@ static std::string SkPictureTracingPath() {
   metrics->padding_top =
       [UIApplication sharedApplication].statusBarFrame.size.height;
 
-  [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent animated:NO];
+  [[UIApplication sharedApplication]
+      setStatusBarStyle:UIStatusBarStyleLightContent
+               animated:NO];
   _sky_engine->OnViewportMetricsChanged(metrics.Pass());
 }
 
@@ -175,85 +169,16 @@ static std::string SkPictureTracingPath() {
   self.platformView->SurfaceCreated(self.acceleratedWidget);
 }
 
-- (NSString*)skyInitialLoadURL {
-  NSUserDefaults *standardDefaults = [NSUserDefaults standardUserDefaults];
-  NSString *target = [standardDefaults stringForKey:@"target"];
-  NSString *server = [standardDefaults stringForKey:@"server"];
-  if (server && target) {
-    return [NSString stringWithFormat:@"http://%@/%@", server, target];
-  }
-  return [NSBundle mainBundle].infoDictionary[@"org.domokit.sky.load_url"];
-}
-
-- (NSString*)skyInitialBundleURL {
-  NSString *flxBundlePath = [[NSBundle mainBundle] pathForResource:@"app" ofType:@"flx"];
-#ifndef NDEBUG
-  NSFileManager *fileManager = [NSFileManager defaultManager];
-  NSError *error = nil;
-  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
-  NSString *documentsDirectory = [paths objectAtIndex:0];
-  NSString *flxDocsPath = [documentsDirectory stringByAppendingPathComponent:@"app.flx"];
-
-  // Write an empty file to help identify the correct simulator app by its bundle id. See sky_tool for its use.
-  NSString *bundleIDPath = [documentsDirectory stringByAppendingPathComponent:[[NSBundle mainBundle] bundleIdentifier]];
-  NSData *data = [[NSData alloc] initWithBytes:"" length:0];
-  if (![data writeToFile:bundleIDPath options:NSDataWritingAtomic error:&error]) {
-      NSLog(@"Couldn't write the bundle id file %@: auto reloading on the iOS simulator won't work\n%@", bundleIDPath, error);
-  }
-
-  if (flxBundlePath != nil && [fileManager fileExistsAtPath:flxDocsPath] == NO) {
-    if ([fileManager copyItemAtPath:flxBundlePath toPath:flxDocsPath error:&error]) {
-      return flxDocsPath;
-    }
-    NSLog(@"Error encountered copying app.flx from the Bundle to the Documents directory. Dynamic reloading will not be possible. %@", error);
-    return flxBundlePath;
-  }
-  return flxDocsPath;
-#endif
-  return flxBundlePath;
-}
-
 - (void)connectToEngineAndLoad {
   auto interface_request = mojo::GetProxy(&_sky_engine);
   self.platformView->ConnectToEngine(interface_request.Pass());
-
-  NSString *endpoint = self.skyInitialBundleURL;
-  if (endpoint.length > 0) {
-#ifndef NDEBUG
-    _document_watcher = [[DocumentWatcher alloc] initWithDocumentPath:endpoint callbackBlock:^{
-      mojo::String string(endpoint.UTF8String);
-      _sky_engine->RunFromBundle(string);
-    }];
-#endif
-    // Load from bundle
-    mojo::String string(endpoint.UTF8String);
-    _sky_engine->RunFromBundle(string);
-    return;
-  }
-
-  endpoint = self.skyInitialLoadURL;
-  if (endpoint.length > 0) {
-    // Load from URL
-    mojo::String string(endpoint.UTF8String);
-    _sky_engine->RunFromNetwork(string);
-    return;
-  }
+  _sky_engine->RunFromPrecompiledSnapshot();
 }
 
 - (void)notifySurfaceDestruction {
   self.platformView->SurfaceDestroyed();
 }
 
-#ifndef NDEBUG
-- (void)didMoveToWindow {
-  if (self.window == nil) {
-    [_document_watcher cancel];
-    [_document_watcher release];
-    _document_watcher = nil;
-  }
-}
-#endif
-
 #pragma mark - UIResponder overrides for raw touches
 
 - (void)dispatchTouches:(NSSet*)touches phase:(UITouchPhase)phase {

sky/shell/ui/engine.cc

@@ -181,6 +181,13 @@ void Engine::RunFromSnapshotStream(
   sky_view_->SetDisplayMetrics(display_metrics_);
 }
 
+void Engine::RunFromPrecompiledSnapshot() {
+  sky_view_ = blink::SkyView::Create(this);
+  sky_view_->CreateView("Sky");
+  sky_view_->RunFromPrecompiledSnapshot();
+  sky_view_->SetDisplayMetrics(display_metrics_);
+}
+
 void Engine::RunFromNetwork(const mojo::String& url) {
   dart_library_provider_.reset(
       new DartLibraryProviderNetwork(network_service_.get()));

sky/shell/ui/engine.h

@@ -74,6 +74,7 @@ class Engine : public UIDelegate,
   void RunFromNetwork(const mojo::String& url) override;
   void RunFromFile(const mojo::String& main,
                    const mojo::String& package_root) override;
+  void RunFromPrecompiledSnapshot() override;
   void RunFromSnapshot(const mojo::String& path) override;
   void RunFromBundle(const mojo::String& path) override;
 

sky/tools/gn

@@ -48,6 +48,7 @@ def to_gn_args(args):
         if args.simulator:
             gn_args['use_libjpeg_turbo'] = False
         gn_args['use_ios_simulator'] = args.simulator
+        gn_args['dart_target_arch'] = "arm64"
     else:
         gn_args['use_aura'] = False
         gn_args['use_glib'] = False

sky/tools/sky_build.py

@@ -22,6 +22,9 @@ def main():
     parser.add_argument('--output-file', type=str)
     parser.add_argument('--package-root', type=str)
     parser.add_argument('--snapshot', type=str)
+    parser.add_argument('--precompiled', dest='precompiled', action='store_true')
+    parser.set_defaults(precompiled=False)
+
     args = parser.parse_args()
 
     command = [
@@ -36,6 +39,11 @@ def main():
         '--private-key', os.path.abspath(os.path.join(args.package_root, '..', 'privatekey.der')),
     ]
 
+    if args.precompiled:
+        command += [
+            '--precompiled'
+        ]
+
     if args.manifest:
         command += ['--manifest', os.path.abspath(args.manifest)]