Define frame subscription interface and implementation on Mac

content/port/browser/render_widget_host_view_port.h

Index: content/port/browser/render_widget_host_view_port.h
diff --git a/content/port/browser/render_widget_host_view_port.h b/content/port/browser/render_widget_host_view_port.h
index 05470af40017ecdf764b275a8d176d5a8e7e6f61..8907d1da25b06bb62a3093853dee763815951fc0 100644
--- a/content/port/browser/render_widget_host_view_port.h
+++ b/content/port/browser/render_widget_host_view_port.h
@@ -47,6 +47,7 @@ struct WebScreenInfo;
 
 namespace content {
 class BackingStore;
+class RenderWidgetHostViewFrameSubscriber;
 class SmoothScrollGesture;
 struct NativeWebKeyboardEvent;
 
@@ -198,6 +199,19 @@ class CONTENT_EXPORT RenderWidgetHostViewPort : public RenderWidgetHostView,
   // IsSurfaceAvailableForCopy() and HasAcceleratedSurface().
   virtual bool CanCopyToVideoFrame() const = 0;
 
+  // Return true if frame subscription is supported on this platform.
+  virtual bool CanSubscribeFrame() const = 0;
+
+  // Begin subscribing for presentation events and captured frames.
+  // |subscriber| is now owned by this object, it will be called only on the
+  // UI thread.
+  virtual void BeginFrameSubscription(
+      RenderWidgetHostViewFrameSubscriber* subscriber) = 0;
+
+  // End subscribing for frame presentation events. FrameSubscriber will be
+  // deleted after this call.
+  virtual void EndFrameSubscription() = 0;
+
   // Called when accelerated compositing state changes.
   virtual void OnAcceleratedCompositingStateChange() = 0;
   // |params.window| and |params.surface_id| indicate which accelerated