Conditionally enable accessibility (#2785)

Previously we enabled accessibility unconditionally on iOS, which is more
expensive than necessary. We still enable it unconditionally on the simulator
because there's no API for determining whether accessibility is needed on the
simulator.

sky/shell/platform/ios/framework/Source/FlutterView.h

@@ -5,14 +5,10 @@
 #ifndef SKY_SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTER_VIEW_H_
 #define SKY_SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTER_VIEW_H_
 
-#include "mojo/public/interfaces/application/service_provider.mojom.h"
-
 #include <UIKit/UIKit.h>
 
 @interface FlutterView : UIView
 
-- (void)withAccessibility:(mojo::ServiceProvider*)serviceProvider;
-
 @end
 
 #endif  // SKY_SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTER_VIEW_H_

sky/shell/platform/ios/framework/Source/FlutterView.mm

@@ -4,20 +4,11 @@
 
 #include "sky/shell/platform/ios/framework/Source/FlutterView.h"
 
-#include "base/memory/weak_ptr.h"
-#include "sky/shell/platform/ios/framework/Source/accessibility_bridge.h"
-
 @interface FlutterView ()<UIInputViewAudioFeedback>
 
 @end
 
-@implementation FlutterView {
-  std::unique_ptr<sky::shell::AccessibilityBridge> _accessibilityBridge;
-}
-
-- (void)withAccessibility:(mojo::ServiceProvider*)serviceProvider {
-  _accessibilityBridge.reset(new sky::shell::AccessibilityBridge(self, serviceProvider));
-}
+@implementation FlutterView
 
 - (void)layoutSubviews {
   CGFloat screenScale = [UIScreen mainScreen].scale;

sky/shell/platform/ios/framework/Source/FlutterViewController.mm

@@ -18,6 +18,7 @@
 #include "sky/services/platform/app_messages.mojom.h"
 #include "sky/services/platform/ios/system_chrome_impl.h"
 #include "sky/services/semantics/semantics.mojom.h"
+#include "sky/shell/platform/ios/framework/Source/accessibility_bridge.h"
 #include "sky/shell/platform/ios/framework/Source/application_messages_impl.h"
 #include "sky/shell/platform/ios/framework/Source/flutter_touch_mapper.h"
 #include "sky/shell/platform/ios/framework/Source/FlutterDartProject_Internal.h"
@@ -50,6 +51,7 @@ void FlutterInit(int argc, const char* argv[]) {
   std::unique_ptr<sky::shell::ShellView> _shellView;
   sky::SkyEnginePtr _engine;
   mojo::ServiceProviderPtr _dartServices;
+  std::unique_ptr<sky::shell::AccessibilityBridge> _accessibilityBridge;
   flutter::platform::ApplicationMessagesPtr _appMessageSender;
   sky::shell::ApplicationMessagesImpl _appMessageReceiver;
   BOOL _initialized;
@@ -147,6 +149,11 @@ void FlutterInit(int argc, const char* argv[]) {
              selector:@selector(onLocaleUpdated:)
                  name:NSCurrentLocaleDidChangeNotification
                object:nil];
+
+  [center addObserver:self
+             selector:@selector(onVoiceOverChanged:)
+                 name:UIAccessibilityVoiceOverStatusChanged
+               object:nil];
 }
 
 #pragma mark - Initializing the engine
@@ -226,13 +233,14 @@ static void DynamicServiceResolve(void* baton,
 
 - (void)loadView {
   FlutterView* surface = [[FlutterView alloc] init];
-  [surface withAccessibility:_dartServices.get()];
 
   self.view = surface;
   self.view.multipleTouchEnabled = YES;
   self.view.autoresizingMask =
       UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
 
+  [self onVoiceOverChanged:nil];
+
   [surface release];
 }
 
@@ -420,6 +428,27 @@ static inline PointerTypeMapperPhase PointerTypePhaseFromUITouchPhase(
   return _orientationPreferences;
 }
 
+#pragma mark - Accessibility
+
+- (void)onVoiceOverChanged:(NSNotification*)notification {
+#if TARGET_OS_SIMULATOR
+  // There doesn't appear to be any way to determine whether the accessibility
+  // inspector is enabled on the simulator. We conservatively always turn on the
+  // accessibility bridge in the simulator.
+  bool enable = true;
+#else
+  bool enable = UIAccessibilityIsVoiceOverRunning();
+#endif
+  if (enable) {
+    if (!_accessibilityBridge) {
+      _accessibilityBridge.reset(
+        new sky::shell::AccessibilityBridge(self.view, _dartServices.get()));
+    }
+  } else {
+    _accessibilityBridge = nullptr;
+  }
+}
+
 #pragma mark - Locale updates
 
 - (void)onLocaleUpdated:(NSNotification*)notification {

sky/shell/platform/ios/framework/Source/accessibility_bridge.h

@@ -49,12 +49,12 @@ namespace shell {
 
 class AccessibilityBridge final : public semantics::SemanticsListener {
  public:
-  AccessibilityBridge(FlutterView*, mojo::ServiceProvider*);
+  AccessibilityBridge(UIView*, mojo::ServiceProvider*);
   ~AccessibilityBridge() override;
 
   void UpdateSemanticsTree(mojo::Array<semantics::SemanticsNodePtr>) override;
 
-  FlutterView* view() { return view_; }
+  UIView* view() { return view_; }
   semantics::SemanticsServer* server() { return semantics_server_.get(); }
 
  private:
@@ -65,7 +65,7 @@ class AccessibilityBridge final : public semantics::SemanticsListener {
   void RemoveSemanticObject(SemanticObject* node,
                             std::set<SemanticObject*>* updated_objects);
 
-  FlutterView* view_;
+  UIView* view_;
   semantics::SemanticsServerPtr semantics_server_;
   std::unordered_map<int, SemanticObject*> objects_;
 

sky/shell/platform/ios/framework/Source/accessibility_bridge.mm

@@ -283,7 +283,7 @@ struct Geometry {
 namespace sky {
 namespace shell {
 
-AccessibilityBridge::AccessibilityBridge(FlutterView* view,
+AccessibilityBridge::AccessibilityBridge(UIView* view,
                                          mojo::ServiceProvider* serviceProvider)
     : view_(view), binding_(this) {
   mojo::ConnectToService(serviceProvider, mojo::GetProxy(&semantics_server_));
@@ -302,6 +302,7 @@ AccessibilityBridge::~AccessibilityBridge() {
 
 void AccessibilityBridge::UpdateSemanticsTree(
     mojo::Array<semantics::SemanticsNodePtr> nodes) {
+  LOG(INFO) << "UpdateSemanticsTree";
   std::set<SemanticObject*> updated_objects;
   std::set<SemanticObject*> removed_objects;