Make OffscreenCanvas animation in sync with its placeholder canvas's parent frame rate

content/browser/renderer_host/offscreen_canvas_compositor_frame_sink_provider_impl.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/offscreen_canvas_compositor_frame_sink_provider_impl.h"
 
 #include "base/memory/ptr_util.h"
 #include "content/browser/compositor/surface_utils.h"
 #include "content/browser/renderer_host/offscreen_canvas_compositor_frame_sink.h"
+#include "content/browser/renderer_host/offscreen_canvas_surface_manager.h"
 #include "mojo/public/cpp/bindings/strong_binding.h"
 
 namespace content {
 
 OffscreenCanvasCompositorFrameSinkProviderImpl::
     OffscreenCanvasCompositorFrameSinkProviderImpl() {}
 
 OffscreenCanvasCompositorFrameSinkProviderImpl::
     ~OffscreenCanvasCompositorFrameSinkProviderImpl() {}
 
 void OffscreenCanvasCompositorFrameSinkProviderImpl::Add(
     blink::mojom::OffscreenCanvasCompositorFrameSinkProviderRequest request) {
   bindings_.AddBinding(this, std::move(request));
 }
 
 void OffscreenCanvasCompositorFrameSinkProviderImpl::CreateCompositorFrameSink(
     const cc::FrameSinkId& frame_sink_id,
     cc::mojom::MojoCompositorFrameSinkClientPtr client,
     cc::mojom::MojoCompositorFrameSinkRequest request) {
   compositor_frame_sinks_[frame_sink_id] =
       base::MakeUnique<OffscreenCanvasCompositorFrameSink>(
           this, frame_sink_id, std::move(request), std::move(client));
+
+  OffscreenCanvasSurfaceManager::GetInstance()->RegisterFrameSinkToParent(
+      frame_sink_id);
 }
 
 cc::SurfaceManager*
 OffscreenCanvasCompositorFrameSinkProviderImpl::GetSurfaceManager() {
   return content::GetSurfaceManager();
 }
 
 void OffscreenCanvasCompositorFrameSinkProviderImpl::
     OnCompositorFrameSinkClientConnectionLost(
         const cc::FrameSinkId& frame_sink_id) {
   compositor_frame_sinks_.erase(frame_sink_id);
 }
 
+void OffscreenCanvasCompositorFrameSinkProviderImpl::
+    OnCompositorFrameSinkClientDestroyed(const cc::FrameSinkId& frame_sink_id) {
+  OffscreenCanvasSurfaceManager::GetInstance()->UnregisterFrameSinkFromParent(
+      frame_sink_id);

[Fady Samuel, 2017/01/19 17:10:53]

I don't think this is necessary. compositor_frame_sinks_ owns the
CompositorFrameSink.

I think you can simply put this line just below
compositor_frame_sinks_.erase(frame_sink_id); in
OffscreenCanvasCompositorFrmaeSinkProviderImpl::OnCompositorFrameSinkClientConnectionLost.

[xlai (Olivia), 2017/01/19 19:14:34]

I just double check, OnConnectionLost is not fired when I close the window.

The current situation is that OnCompositorFrameSinkClientConnectionLost is not
fired before SurfaceManager is destroyed, resulting in an assert failure in
DCHECK_EQ(frame_sink_source_map_.size(), 0u); in SurfaceManager's destructor,
when I close down the window. So I think an explicit call to unregister is still
needed in compositorFrameSink's own destructor, until we figure out why the
OnConnectionLost itself is not sufficient. I will put a TODO inside
OnCompositorFrameSinkConnectionLost.

+}
+
 }  // namespace content