Implement compositor thread VSync aligned event queue

ui/events/blink/input_handler_proxy.h

Index: ui/events/blink/input_handler_proxy.h
diff --git a/ui/events/blink/input_handler_proxy.h b/ui/events/blink/input_handler_proxy.h
index 84df86dcfed637b4b836587e72fd0fd7410aff4b..048895452c5265f4fa3b19dbdf784223bc40e80b 100644
--- a/ui/events/blink/input_handler_proxy.h
+++ b/ui/events/blink/input_handler_proxy.h
@@ -14,6 +14,7 @@
 #include "third_party/WebKit/public/platform/WebGestureCurveTarget.h"
 #include "third_party/WebKit/public/platform/WebInputEvent.h"
 #include "third_party/WebKit/public/web/WebActiveWheelFlingParameters.h"
+#include "ui/events/blink/blink_features.h"
 #include "ui/events/blink/input_scroll_elasticity_controller.h"
 #include "ui/events/blink/scoped_web_input_event.h"
 #include "ui/events/blink/synchronous_input_handler_proxy.h"
@@ -22,8 +23,11 @@ namespace ui {
 
 namespace test {
 class InputHandlerProxyTest;
+class InputHandlerProxyEventQueueTest;
 }
 
+class CompositorThreadEventQueue;
+class EventWithCallback;
 class InputHandlerProxyClient;
 class InputScrollElasticityController;
 class SynchronousInputHandler;
@@ -79,6 +83,7 @@ class InputHandlerProxy
       float page_scale_factor,
       float min_page_scale_factor,
       float max_page_scale_factor) override;
+  void DeliverInputForBeginFrame() override;
 
   // SynchronousInputHandlerProxy implementation.
   void SetOnlySynchronouslyAnimateRootFlings(
@@ -103,6 +108,10 @@ class InputHandlerProxy
 
  private:
   friend class test::InputHandlerProxyTest;
+  friend class test::InputHandlerProxyEventQueueTest;
+
+  void DispatchSingleInputEvent(std::unique_ptr<EventWithCallback>);
+  void DispatchQueuedInputEvents();
 
   // Helper functions for handling more complicated input events.
   EventDisposition HandleMouseWheel(
@@ -227,6 +236,10 @@ class InputHandlerProxy
   // supporting overscroll IPC notifications due to fling animation updates.
   std::unique_ptr<DidOverscrollParams> current_overscroll_params_;
 
+  std::unique_ptr<CompositorThreadEventQueue> event_queue_;
+  bool has_ongoing_compositor_scroll_pinch_;
+  bool compositor_event_queue_enabled_;
+
   DISALLOW_COPY_AND_ASSIGN(InputHandlerProxy);
 };