Early terminate WebGL markContextChanged calls when appropriate

third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1316 matching lines @@
   ASSERT(drawingBuffer());
   m_drawingBuffer->beginDestruction();
   m_drawingBuffer.clear();
 }
 
 void WebGLRenderingContextBase::markContextChanged(
     ContentChangeType changeType) {
   if (m_framebufferBinding || isContextLost())
     return;
 
-  drawingBuffer()->markContentsChanged();
+  if (!drawingBuffer()->markContentsChanged() && m_markedCanvasDirty) {

[Ken Russell (switch to Gerrit), 2016/11/29 04:31:16]

We should really revisit and clean up the maintenance of m_markedCanvasDirty,
which seems to only be set to false on the software compositing path.

+    return;
+  }
 
   if (!canvas())
     return;
 
   LayoutBox* layoutBox = canvas()->layoutBox();
   if (layoutBox && layoutBox->hasAcceleratedCompositing()) {
     m_markedCanvasDirty = true;
     canvas()->clearCopiedImage();
     layoutBox->contentChanged(changeType);
   } else {
@@ skipping 6421 matching lines @@
 
 void WebGLRenderingContextBase::getHTMLOrOffscreenCanvas(
     HTMLCanvasElementOrOffscreenCanvas& result) const {
   if (canvas())
     result.setHTMLCanvasElement(canvas());
   else
     result.setOffscreenCanvas(getOffscreenCanvas());
 }
 
 }  // namespace blink