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

Source/platform/graphics/RegionTracker.h

 /*
  * Copyright (c) 2012, 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 10 matching lines @@
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef OpaqueRegionSkia_h
-#define OpaqueRegionSkia_h
+#ifndef RegionTracker_h
+#define RegionTracker_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/IntRect.h"
-
-#include "SkBitmap.h"
-#include "SkCanvas.h"
-#include "SkPaint.h"
-#include "SkPoint.h"
-#include "SkRect.h"
+#include "third_party/skia/include/core/SkBitmap.h"
+#include "third_party/skia/include/core/SkCanvas.h"
+#include "third_party/skia/include/core/SkPaint.h"
+#include "third_party/skia/include/core/SkPoint.h"
+#include "third_party/skia/include/core/SkRect.h"
 
 namespace blink {
 class GraphicsContext;
 
+enum RegionTrackingMode {
+    TrackOpaqueRegion,
+    TRackOverwriteRegion
+};
+
 // This class is an encapsulation of functionality for GraphicsContext, and its methods are mirrored
 // there for the outside world. It tracks paints and computes what area will be opaque.
-class PLATFORM_EXPORT OpaqueRegionSkia FINAL {
+class PLATFORM_EXPORT RegionTracker FINAL {
 public:
-    OpaqueRegionSkia();
+    RegionTracker();
 
     // The resulting opaque region as a single rect.
     IntRect asRect() const;
 
     void pushCanvasLayer(const SkPaint*);
     void popCanvasLayer(const GraphicsContext*);
 
     void setImageMask(const SkRect& imageOpaqueRect);
 
+    enum RegionType {
+        Opaque,
+        Overwrite
+    };
+
+    // Set this to true to track regions that occlude the destination instead of only regions that produce opaque pixels.
+    void setTrackedRegionType(RegionType type) { m_trackedRegionType = type; }
+
     enum DrawType {
         FillOnly,
         FillOrStroke
     };
 
     void didDrawRect(const GraphicsContext*, const SkRect&, const SkPaint&, const SkBitmap* sourceBitmap);
     void didDrawPath(const GraphicsContext*, const SkPath&, const SkPaint&);
     void didDrawPoints(const GraphicsContext*, SkCanvas::PointMode, int numPoints, const SkPoint[], const SkPaint&);
     void didDrawBounded(const GraphicsContext*, const SkRect&, const SkPaint&);
     void didDrawUnbounded(const GraphicsContext*, const SkPaint&, DrawType);
@@ skipping 19 matching lines @@
 private:
     void didDraw(const GraphicsContext*, const SkRect&, const SkPaint&, const SkBitmap* sourceBitmap, bool fillsBounds, DrawType);
     void applyOpaqueRegionFromLayer(const GraphicsContext*, const SkRect& layerOpaqueRect, const SkPaint&);
     void markRectAsOpaque(const SkRect&);
     void markRectAsNonOpaque(const SkRect&);
     void markAllAsNonOpaque();
 
     SkRect& currentTrackingOpaqueRect();
 
     SkRect m_opaqueRect;
+    RegionType m_trackedRegionType;
 
     Vector<CanvasLayerState, 3> m_canvasLayerStack;
 };
 
 }
-#endif // OpaqueRegionSkia_h
+#endif // RegionTracker_h