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

Source/platform/graphics/GraphicsContext.h

 /*
  * Copyright (C) 2003, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008-2009 Torch Mobile, Inc.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 19 matching lines @@
 
 #include "platform/PlatformExport.h"
 #include "platform/fonts/Font.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/graphics/DashArray.h"
 #include "platform/graphics/DrawLooperBuilder.h"
 #include "platform/graphics/ImageBufferSurface.h"
 #include "platform/graphics/ImageOrientation.h"
 #include "platform/graphics/GraphicsContextAnnotation.h"
 #include "platform/graphics/GraphicsContextState.h"
-#include "platform/graphics/skia/OpaqueRegionSkia.h"
+#include "platform/graphics/RegionTracker.h"
 #include "wtf/FastAllocBase.h"
 #include "wtf/Forward.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/PassOwnPtr.h"
 
 class SkBitmap;
 class SkPaint;
 class SkPath;
 class SkRRect;
 struct SkRect;
@@ skipping 165 matching lines @@
     // context. Bitmap shouldn't be resampled when printing to keep the best
     // possible quality.
     bool printing() const { return m_printing; }
     void setPrinting(bool printing) { m_printing = printing; }
 
     bool isAccelerated() const { return m_accelerated; }
     void setAccelerated(bool accelerated) { m_accelerated = accelerated; }
 
     // The opaque region is empty until tracking is turned on.
     // It is never clerared by the context.
-    void setTrackOpaqueRegion(bool track) { m_trackOpaqueRegion = track; }
-    const OpaqueRegionSkia& opaqueRegion() const { return m_opaqueRegion; }
+    enum RegionTrackingMode {
+        RegionTrackingDisabled = 0,
+        RegionTrackingOpaque,
+        RegionTrackingOverwrite
+    };
+    void setRegionTrackingMode(RegionTrackingMode);
+    bool regionTrackingEnabled() { return m_regionTrackingMode != RegionTrackingDisabled; }
+    const RegionTracker& opaqueRegion() const { return m_trackedRegion; }
 
     // The text region is empty until tracking is turned on.
     // It is never clerared by the context.
     void setTrackTextRegion(bool track) { m_trackTextRegion = track; }
     const SkRect& textRegion() const { return m_textRegion; }
 
     bool updatingControlTints() const { return m_updatingControlTints; }
     void setUpdatingControlTints(bool updatingTints) { m_updatingControlTints = updatingTints; }
 
     AnnotationModeFlags annotationMode() const { return m_annotationMode; }
@@ skipping 275 matching lines @@
 
     struct RecordingState;
     Vector<RecordingState> m_recordingStateStack;
 
 #if ENABLE(ASSERT)
     unsigned m_annotationCount;
     unsigned m_layerCount;
     bool m_disableDestructionChecks;
 #endif
     // Tracks the region painted opaque via the GraphicsContext.
-    OpaqueRegionSkia m_opaqueRegion;
+    RegionTracker m_trackedRegion;
 
     // Tracks the region where text is painted via the GraphicsContext.
     SkRect m_textRegion;
 
     unsigned m_disabledState;
 
     float m_deviceScaleFactor;
 
     // Activation for the above region tracking features
-    bool m_trackOpaqueRegion : 1;
+    unsigned m_regionTrackingMode : 2;
     bool m_trackTextRegion : 1;
 
     // FIXME: Make this go away: crbug.com/236892
     bool m_updatingControlTints : 1;
     bool m_accelerated : 1;
     bool m_isCertainlyOpaque : 1;
     bool m_printing : 1;
     bool m_antialiasHairlineImages : 1;
 };
 
 } // namespace blink
 
 #endif // GraphicsContext_h