Early terminate WebGL markContextChanged calls when appropriate

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h

 /*
  * Copyright (c) 2010, Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 144 matching lines @@
   // the resolved color buffer bound to GL_READ_FRAMEBUFFER and
   // GL_DRAW_FRAMEBUFFER.
   void resolveAndBindForReadAndDraw();
 
   bool multisample() const;
 
   bool discardFramebufferSupported() const {
     return m_discardFramebufferSupported;
   }
 
-  void markContentsChanged();
+  // Returns false if the contents had previously been marked as changed and
+  // have not yet been committed.
+  bool markContentsChanged();
   void setBufferClearNeeded(bool);
   bool bufferClearNeeded() const;
   void setIsHidden(bool);
   void setFilterQuality(SkFilterQuality);
 
   // Whether the target for draw operations has format GL_RGBA, but is
   // emulating format GL_RGB. When the target's storage is first
   // allocated, its alpha channel must be cleared to 1. All future drawing
   // operations must use a color mask with alpha=GL_FALSE.
   bool requiresAlphaChannelToBePreserved();
@@ skipping 338 matching lines @@
   // RuntimeEnabledFeatures::webGLImageChromiumEnabled() call with
   // shouldUseChromiumImage() calls, and set m_chromiumImageUsage to
   // DisallowChromiumImage in the case of OffscreenCanvas.
   ChromiumImageUsage m_chromiumImageUsage;
   bool shouldUseChromiumImage();
 };
 
 }  // namespace blink
 
 #endif  // DrawingBuffer_h