Early terminate WebGL markContextChanged calls when appropriate

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

 /*
  * 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 146 matching lines @@
   TRACE_EVENT_INSTANT0("test_gpu", "DrawingBufferCreation",
                        TRACE_EVENT_SCOPE_GLOBAL);
 }
 
 DrawingBuffer::~DrawingBuffer() {
   DCHECK(m_destructionInProgress);
   m_layer.reset();
   m_contextProvider.reset();
 }
 
-void DrawingBuffer::markContentsChanged() {
-  m_contentsChanged = true;
-  m_contentsChangeCommitted = false;
+bool DrawingBuffer::markContentsChanged() {
+  if (m_contentsChangeCommitted || !m_contentsChanged) {
+    m_contentsChangeCommitted = false;
+    m_contentsChanged = true;
+    return true;
+  }
+  return false;
 }
 
 bool DrawingBuffer::bufferClearNeeded() const {
   return m_bufferClearNeeded;
 }
 
 void DrawingBuffer::setBufferClearNeeded(bool flag) {
   if (m_preserveDrawingBuffer == Discard) {
     m_bufferClearNeeded = flag;
   } else {
@@ skipping 1077 matching lines @@
   if (m_pixelUnpackBufferBindingDirty)
     client->DrawingBufferClientRestorePixelUnpackBufferBinding();
 }
 
 bool DrawingBuffer::shouldUseChromiumImage() {
   return RuntimeEnabledFeatures::webGLImageChromiumEnabled() &&
          m_chromiumImageUsage == AllowChromiumImage;
 }
 
 }  // namespace blink