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

Source/platform/graphics/RecordingImageBufferSurfaceTest.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/GraphicsContext.h"
 #include "platform/graphics/ImageBuffer.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkPictureRecorder.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/RefPtr.h"
 
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 
@@ skipping 54 matching lines @@
         m_testSurface->didClearCanvas();
         m_testSurface->willUse();
         m_testSurface->getPicture();
         expectDisplayListEnabled(true);
         // clear after use
         m_testSurface->willUse();
         m_testSurface->didClearCanvas();
         m_testSurface->getPicture();
         expectDisplayListEnabled(true);
     }
+
+    void testClearRect()
+    {
+        m_testSurface->initializeCurrentFrame();
+        m_testSurface->getPicture();
+        m_imageBuffer->context()->clearRect(FloatRect(FloatPoint(0, 0), FloatSize(m_testSurface->size())));
+        m_testSurface->willUse();
+        m_testSurface->getPicture();
+        expectDisplayListEnabled(true);
+    }
 private:
     void expectDisplayListEnabled(bool displayListEnabled)
     {
         EXPECT_EQ(displayListEnabled, (bool)m_testSurface->m_currentFrame.get());
         EXPECT_EQ(!displayListEnabled, (bool)m_testSurface->m_rasterCanvas.get());
     }
 
     RecordingImageBufferSurface* m_testSurface;
     OwnPtr<ImageBuffer> m_imageBuffer;
 };
@@ skipping 18 matching lines @@
 TEST_F(RecordingImageBufferSurfaceTest, testAnimatedWithoutClear)
 {
     testAnimatedWithoutClear();
 }
 
 TEST_F(RecordingImageBufferSurfaceTest, testAnimatedWithClear)
 {
     testAnimatedWithClear();
 }
 
+TEST_F(RecordingImageBufferSurfaceTest, testClearRect)
+{
+    testClearRect();
+}
+
 } // namespace