Early terminate WebGL markContextChanged calls when appropriate.

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

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
index 82f55a9e8de826c01a1d1b75256d58fe05b013e0..fa13e0066174a0e64868545d00badea66d905ab6 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -172,10 +172,14 @@ DrawingBuffer::~DrawingBuffer()
     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