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

content/browser/renderer_host/offscreen_canvas_compositor_frame_sink.cc

Index: content/browser/renderer_host/offscreen_canvas_compositor_frame_sink.cc
diff --git a/content/browser/renderer_host/offscreen_canvas_compositor_frame_sink.cc b/content/browser/renderer_host/offscreen_canvas_compositor_frame_sink.cc
index 5717d03773b2bb1f13af95819701a97a1cee8a5e..0c2ddfbefce685152e1faf52a24c6bc92be46d3e 100644
--- a/content/browser/renderer_host/offscreen_canvas_compositor_frame_sink.cc
+++ b/content/browser/renderer_host/offscreen_canvas_compositor_frame_sink.cc
@@ -8,6 +8,7 @@
 #include "cc/surfaces/surface.h"
 #include "cc/surfaces/surface_manager.h"
 #include "content/browser/renderer_host/offscreen_canvas_compositor_frame_sink_provider_impl.h"
+#include "content/browser/renderer_host/offscreen_canvas_surface_manager.h"
 #include "mojo/public/cpp/bindings/strong_binding.h"
 
 namespace content {
@@ -28,9 +29,15 @@ OffscreenCanvasCompositorFrameSink::OffscreenCanvasCompositorFrameSink(
   binding_.set_connection_error_handler(
       base::Bind(&OffscreenCanvasCompositorFrameSink::OnClientConnectionLost,
                  base::Unretained(this)));
+
+  OffscreenCanvasSurfaceManager::GetInstance()->RegisterFrameSinkToItsParent(

[Fady Samuel, 2017/01/19 04:05:43]

Maybe move this to
OffscreenCanvasCompositorFrameSinkProviderImpl::CreateCompositorFrameSink?

The reason being I want this class to continue to look like
GpuCompositorFrameSink so we can merge those two soon.

[xlai (Olivia), 2017/01/19 16:43:56]

Done.

+      frame_sink_id);
 }
 
-OffscreenCanvasCompositorFrameSink::~OffscreenCanvasCompositorFrameSink() {}
+OffscreenCanvasCompositorFrameSink::~OffscreenCanvasCompositorFrameSink() {
+  OffscreenCanvasSurfaceManager::GetInstance()
+      ->UnregisterFrameSinkFromItsParent(support_.frame_sink_id());

[Fady Samuel, 2017/01/19 04:05:43]

Maybe move this to
OffscreenCanvasCompositorFrameSinkProviderImpl::OnCompositorFrameSinkClientConnectionLost?

The reason being I want this class to continue to look like
GpuCompositorFrameSink so we can merge those two soon.

[xlai (Olivia), 2017/01/19 16:43:56]

Simply moving this to OnCompositorFrameSinkClientConnectionLost will not work,
because OnCompositorFrameSinkClientConnectionLost is not fired when
OffscreenCanvasCompositorFrameSink is destroyed normally (i.e. closing down the
window), which will then result in assert failure in SurfaceManager's
destructor.

My workaround is to introduce
OffscreenCanvasCompositorFrameSinkProviderImpl::OnCompositorFrameSinkClientDestroyed
and call that when compositorframesink is destroyed. With that, I can avoid
seeing the assert error when I close down the window.

+}
 
 void OffscreenCanvasCompositorFrameSink::SetNeedsBeginFrame(
     bool needs_begin_frame) {