The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fa845ac545a12d519ab5cb7d7ba5d9fd57ae2a0c

commit fa845ac545a12d519ab5cb7d7ba5d9fd57ae2a0c
Author: junov <junov@chromium.org>
Date: Fri Apr 28 16:26:27 2017

Adjust OffscreenCanvas throttling to allow two frames of backlog

The throttling fix landed in https://codereview.chromium.org/2817603004/
has severely impacted rendering throughput due to the delay in
compositor round trips.  To avoid blocking the renderer script's
animation loop, we need to allow the rendering proceed when there
is still a pending frame.

BUG= 716138 

Review-Url: https://codereview.chromium.org/2848553003
Cr-Commit-Position: refs/heads/master@{#468021}

[modify] https://crrev.com/fa845ac545a12d519ab5cb7d7ba5d9fd57ae2a0c/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.cpp
[modify] https://crrev.com/fa845ac545a12d519ab5cb7d7ba5d9fd57ae2a0c/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h