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

Source/platform/graphics/RecordingImageBufferSurfaceTest.cpp

Index: Source/platform/graphics/RecordingImageBufferSurfaceTest.cpp
diff --git a/Source/platform/graphics/RecordingImageBufferSurfaceTest.cpp b/Source/platform/graphics/RecordingImageBufferSurfaceTest.cpp
index 3237ea71b1cac1477f1878462693ed3db99f1c27..ca7a88880d15b7deb823a09f662fcf56644e7208 100644
--- a/Source/platform/graphics/RecordingImageBufferSurfaceTest.cpp
+++ b/Source/platform/graphics/RecordingImageBufferSurfaceTest.cpp
@@ -6,6 +6,7 @@
 
 #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"
@@ -80,6 +81,16 @@ protected:
         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)
     {
@@ -118,4 +129,9 @@ TEST_F(RecordingImageBufferSurfaceTest, testAnimatedWithClear)
     testAnimatedWithClear();
 }
 
+TEST_F(RecordingImageBufferSurfaceTest, testClearRect)
+{
+    testClearRect();
+}
+
 } // namespace