Fix memory leak in display list canvas overdraw optimization.

Source/platform/graphics/RecordingImageBufferSurface.cpp

Index: Source/platform/graphics/RecordingImageBufferSurface.cpp
diff --git a/Source/platform/graphics/RecordingImageBufferSurface.cpp b/Source/platform/graphics/RecordingImageBufferSurface.cpp
index e5e76f60e2e5f5ac2a2f165ca64e2c68de871241..b95c6070d6f30404beeb904381d81960d5700151 100644
--- a/Source/platform/graphics/RecordingImageBufferSurface.cpp
+++ b/Source/platform/graphics/RecordingImageBufferSurface.cpp
@@ -147,7 +147,7 @@ void RecordingImageBufferSurface::willOverwriteCanvas()
     m_previousFramePixelCount = 0;
     if (m_didRecordDrawCommandsInCurrentFrame) {
         // Discard previous draw commands
-        m_currentFrame->endRecording();
+        m_currentFrame->endRecording()->unref();

[danakj, 2015/04/08 20:48:10]

Maybe not, but is there a way to use RefPtr to not have to deal with this kind
of sadness?

[jbroman, 2015/04/08 21:00:13]

drive-by: I'm going to see if we can get endRecording marked with
SK_WARN_UNUSED_RESULT because not using that result is always a memory leak.

         initializeCurrentFrame();
     }
 }