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 154 matching lines @@
 }
 
 DrawingBuffer::~DrawingBuffer()
 {
     ASSERT(m_destructionInProgress);
     ASSERT(m_textureMailboxes.isEmpty());
     m_layer.clear();
     m_contextProvider.clear();
 }
 
-void DrawingBuffer::markContentsChanged()
+bool DrawingBuffer::markContentsChanged()
 {
-    m_contentsChanged = true;
     m_contentsChangeCommitted = false;
+    if (!m_contentsChanged) {
+        m_contentsChanged = true;
+        return true;
+    }
+    return false;
 }
 
 bool DrawingBuffer::bufferClearNeeded() const
 {
     return m_bufferClearNeeded;
 }
 
 void DrawingBuffer::setBufferClearNeeded(bool flag)
 {
     if (m_preserveDrawingBuffer == Discard) {
@@ skipping 814 matching lines @@
 
     if (m_antiAliasingMode == MSAAImplicitResolve)
         m_gl->FramebufferTexture2DMultisampleEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, target, m_colorBuffer.textureId, 0, m_sampleCount);
     else
         m_gl->FramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, target, m_colorBuffer.textureId, 0);
 
     m_gl->BindTexture(GL_TEXTURE_2D, m_texture2DBinding);
 }
 
 } // namespace blink