Oilpan: improve ScrollableArea handling.

Source/core/frame/PinchViewport.h

 /*
  * 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:
  *
  *     * 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 44 matching lines @@
 class GraphicsLayerFactory;
 class IntRect;
 class IntSize;
 class LocalFrame;
 
 // Represents the pinch-to-zoom viewport the user is currently seeing the page through. This
 // class corresponds to the InnerViewport on the compositor. It is a ScrollableArea; it's
 // offset is set through the GraphicsLayer <-> CC sync mechanisms. Its contents is the page's
 // main FrameView, which corresponds to the outer viewport. The inner viewport is always contained
 // in the outer viewport and can pan within it.
-class CORE_EXPORT PinchViewport final : public GraphicsLayerClient, public ScrollableArea {
+class CORE_EXPORT PinchViewport final : public NoBaseWillBeGarbageCollectedFinalized<PinchViewport>, public GraphicsLayerClient, public ScrollableArea {
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(PinchViewport);
 public:
-    static PassOwnPtr<PinchViewport> create(FrameHost& host)
+    static PassOwnPtrWillBeRawPtr<PinchViewport> create(FrameHost& host)
     {
-        return adoptPtr(new PinchViewport(host));
+        return adoptPtrWillBeNoop(new PinchViewport(host));
     }
     virtual ~PinchViewport();
 
+    DECLARE_VIRTUAL_TRACE();
+
     void attachToLayerTree(GraphicsLayer*, GraphicsLayerFactory*);
     GraphicsLayer* rootGraphicsLayer()
     {
         return m_rootTransformLayer.get();
     }
     GraphicsLayer* containerLayer()
     {
         return m_innerViewportContainerLayer.get();
     }
     GraphicsLayer* scrollLayer()
@@ skipping 113 matching lines @@
     virtual void paintContents(const GraphicsLayer*, GraphicsContext&, GraphicsLayerPaintingPhase, const IntRect& inClip) override;
     virtual String debugName(const GraphicsLayer*) override;
 
     void setupScrollbar(WebScrollbar::Orientation);
     FloatPoint clampOffsetToBoundaries(const FloatPoint&);
 
     LocalFrame* mainFrame() const;
 
     FrameHost& frameHost() const
     {
-        return m_frameHost;
+        ASSERT(m_frameHost);
+        return *m_frameHost;
     }
 
-    // TODO(Oilpan): this back reference is safe, but not ideal.
-    // Turning it into a traced Member<> would require moving
-    // ScrollableArea to the heap.
-    FrameHost& m_frameHost;
+    RawPtrWillBeMember<FrameHost> m_frameHost;
     OwnPtr<GraphicsLayer> m_rootTransformLayer;
     OwnPtr<GraphicsLayer> m_innerViewportContainerLayer;
     OwnPtr<GraphicsLayer> m_overscrollElasticityLayer;
     OwnPtr<GraphicsLayer> m_pageScaleLayer;
     OwnPtr<GraphicsLayer> m_innerViewportScrollLayer;
     OwnPtr<GraphicsLayer> m_overlayScrollbarHorizontal;
     OwnPtr<GraphicsLayer> m_overlayScrollbarVertical;
     OwnPtr<WebScrollbarLayer> m_webOverlayScrollbarHorizontal;
     OwnPtr<WebScrollbarLayer> m_webOverlayScrollbarVertical;
 
     // Offset of the pinch viewport from the main frame's origin, in CSS pixels.
     FloatPoint m_offset;
     float m_scale;
     IntSize m_size;
     float m_topControlsAdjustment;
 };
 
 } // namespace blink
 
 #endif // PinchViewport_h