Use observer pattern instead of sniffing SwapCompositorFrame IPC

content/browser/renderer_host/render_widget_host_impl.cc

Index: content/browser/renderer_host/render_widget_host_impl.cc
diff --git a/content/browser/renderer_host/render_widget_host_impl.cc b/content/browser/renderer_host/render_widget_host_impl.cc
index 5caf7eab7947f091d5262799123294bcac397bac..11e46658091734b06a25441bb4421130e138d248 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -2609,6 +2609,10 @@ void RenderWidgetHostImpl::SubmitCompositorFrame(
     return;
   }
 
+  last_frame_metadata_ = frame.metadata.Clone();

[piman, 2017/04/04 17:34:46]

Could we move this to after l.2636? 2 reasons:
1- we don't want to update the metadata if we reject the bad message
2- we modify frame.metadata below, I think we want last_frame_metadata_ to be
consistent with that.

[Saman Sami, 2017/04/04 17:49:54]

Good point.

+  if (delegate_)
+    delegate_->DidReceiveCompositorFrame();

[piman, 2017/04/04 17:34:46]

Should this move to the end of the function, or at least after l.2658? For
consistent state it may be better to signal the observers after the view was
updated.

[Saman Sami, 2017/04/04 17:49:54]

Done.

+
   last_local_surface_id_ = local_surface_id;
   last_frame_size_ = frame_size;
   last_device_scale_factor_ = device_scale_factor;