Treat calls to CanvasRenderingContext2D.clearRect as operations that clear the canvas

Source/platform/graphics/GraphicsContextRecorder.cpp

Index: Source/platform/graphics/GraphicsContextRecorder.cpp
diff --git a/Source/platform/graphics/GraphicsContextRecorder.cpp b/Source/platform/graphics/GraphicsContextRecorder.cpp
index c7152352260043740b4aee4f1534ffd004af3c73..396a967d75ece2c7dea2db0426d82af913384eb9 100644
--- a/Source/platform/graphics/GraphicsContextRecorder.cpp
+++ b/Source/platform/graphics/GraphicsContextRecorder.cpp
@@ -57,7 +57,7 @@ GraphicsContext* GraphicsContextRecorder::record(const IntSize& size, bool isCer
     m_recorder = adoptPtr(new SkPictureRecorder);
     SkCanvas* canvas = m_recorder->beginRecording(size.width(), size.height(), 0, 0);
     m_context = adoptPtr(new GraphicsContext(canvas));
-    m_context->setTrackOpaqueRegion(isCertainlyOpaque);
+    m_context->setRegionTrackingMode(isCertainlyOpaque ? GraphicsContext::RegionTrackingOpaque : GraphicsContext::RegionTrackingDisabled);
     m_context->setCertainlyOpaque(isCertainlyOpaque);
     return m_context.get();
 }