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 cef880da0f1f1bf886c15be64c4dec1bd9304747..b3af584e3fa36295b5cecdc6f0e459bcfa903113 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -156,10 +156,14 @@ DrawingBuffer::~DrawingBuffer()
     m_contextProvider.reset();
 }
 
-void DrawingBuffer::markContentsChanged()
+bool DrawingBuffer::markContentsChanged()
 {
-    m_contentsChanged = true;
-    m_contentsChangeCommitted = false;
+    if (m_contentsChangeCommitted || !m_contentsChanged) {
+        m_contentsChangeCommitted = false;
+        m_contentsChanged = true;
+        return true;
+    }
+    return false;
 }
 
 bool DrawingBuffer::bufferClearNeeded() const