Fix memory leak in display list canvas overdraw optimization.

Source/platform/graphics/RecordingImageBufferSurface.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 
 #include "platform/graphics/RecordingImageBufferSurface.h"
 
 #include "platform/graphics/ExpensiveCanvasHeuristicParameters.h"
 #include "platform/graphics/GraphicsContext.h"
@@ skipping 129 matching lines @@
 }
 
 void RecordingImageBufferSurface::willOverwriteCanvas()
 {
     m_frameWasCleared = true;
     m_previousFrame.clear();
     m_previousFrameHasExpensiveOp = false;
     m_previousFramePixelCount = 0;
     if (m_didRecordDrawCommandsInCurrentFrame) {
         // Discard previous draw commands
-        m_currentFrame->endRecording();
+        adoptRef(m_currentFrame->endRecording());
         initializeCurrentFrame();
     }
 }
 
 void RecordingImageBufferSurface::didDraw(const FloatRect& rect)
 {
     m_didRecordDrawCommandsInCurrentFrame = true;
     IntRect pixelBounds = enclosingIntRect(rect);
     m_currentFramePixelCount += pixelBounds.width() * pixelBounds.height();
 }
@@ skipping 145 matching lines @@
 
 void RecordingImageBufferSurface::setIsHidden(bool hidden)
 {
     if (m_fallbackSurface)
         m_fallbackSurface->setIsHidden(hidden);
     else
         ImageBufferSurface::setIsHidden(hidden);
 }
 
 } // namespace blink