Add hooks for flushing input from BeginFrame dispatch on Aura

content/browser/renderer_host/begin_frame_observer_proxy.h

Index: content/browser/renderer_host/begin_frame_observer_proxy.h
diff --git a/content/browser/renderer_host/begin_frame_observer_proxy.h b/content/browser/renderer_host/begin_frame_observer_proxy.h
index 291d8bb8a96c51430de2e55662cbbfcc09a3899a..fd6e2cbe4d35cbb3a72a6dfbf6460da86b03946a 100644
--- a/content/browser/renderer_host/begin_frame_observer_proxy.h
+++ b/content/browser/renderer_host/begin_frame_observer_proxy.h
@@ -32,6 +32,7 @@ class CONTENT_EXPORT BeginFrameObserverProxy
   ~BeginFrameObserverProxy() override;
 
   void SetNeedsBeginFrames(bool needs_begin_frames);
+  void SetNeedsOneBeginFrame();
 
   void SetCompositor(ui::Compositor* compositor);
   void ResetCompositor();
@@ -51,12 +52,19 @@ class CONTENT_EXPORT BeginFrameObserverProxy
   void OnCompositingShuttingDown(ui::Compositor* compositor) override;
 
  private:
+  void UpdateBeginFrameObservation();
   void StartObservingBeginFrames();
   void StopObservingBeginFrames();
 
   // True when RenderWidget needs a BeginFrame message.
   bool needs_begin_frames_;
 
+  // True when the RenderWidget needs just one BeginFrame message.
+  bool needs_one_begin_frame_;
+
+  // Whether we're subscribed as a BeginFrame observer.
+  bool observing_begin_frames_;
+
   // Used whether to send begin frame to client or not. When |args| from
   // Compositor is different from this, send to client.
   cc::BeginFrameArgs last_sent_begin_frame_args_;