Oilpan: improve ScrollableArea handling.

Source/core/frame/RootFrameViewport.h

 // Copyright 2015 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.
 
 #ifndef RootFrameViewport_h
 #define RootFrameViewport_h
 
 #include "core/CoreExport.h"
 #include "platform/scroll/ScrollableArea.h"
 
 namespace blink {
 
 class LayoutRect;
 
 // ScrollableArea for the root frame's viewport. This class ties together the
 // concepts of layout and visual viewports, used in pinch-to-zoom. This class
 // takes two ScrollableAreas, one for the visual viewport and one for the
 // layout viewport, and delegates and composes the ScrollableArea API as needed
 // between them. For most scrolling APIs, this class will split the scroll up
 // between the two viewports in accord with the pinch-zoom semantics. For other
 // APIs that don't make sense on the combined viewport, the call is delegated to
 // the layout viewport. Thus, we could say this class is a decorator on the
 // FrameView scrollable area that adds pinch-zoom semantics to scrolling.
-class CORE_EXPORT RootFrameViewport final : public ScrollableArea {
+class CORE_EXPORT RootFrameViewport final : public NoBaseWillBeGarbageCollectedFinalized<RootFrameViewport>, public ScrollableArea {
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(RootFrameViewport);
 public:
-    static PassOwnPtr<RootFrameViewport> create(ScrollableArea& visualViewport, ScrollableArea& layoutViewport)
+    static PassOwnPtrWillBeRawPtr<RootFrameViewport> create(ScrollableArea& visualViewport, ScrollableArea& layoutViewport)
     {
-        return adoptPtr(new RootFrameViewport(visualViewport, layoutViewport));
+        return adoptPtrWillBeNoop(new RootFrameViewport(visualViewport, layoutViewport));
     }
 
+    DECLARE_VIRTUAL_TRACE();
+
     // ScrollableArea Implementation
     void setScrollPosition(const DoublePoint&, ScrollType, ScrollBehavior = ScrollBehaviorInstant) override;
     LayoutRect scrollIntoView(
         const LayoutRect& rectInContent,
         const ScrollAlignment& alignX,
         const ScrollAlignment& alignY) override;
     DoubleRect visibleContentRectDouble(IncludeScrollbarsInRect = ExcludeScrollbars) const override;
     IntRect visibleContentRect(IncludeScrollbarsInRect = ExcludeScrollbars) const override;
     bool shouldUseIntegerScrollOffset() const override;
     bool isActive() const override;
@@ skipping 32 matching lines @@
 private:
     RootFrameViewport(ScrollableArea& visualViewport, ScrollableArea& layoutViewport);
 
     DoublePoint scrollOffsetFromScrollAnimators() const;
 
     // If either of the layout or visual viewports are scrolled explicitly (i.e. not
     // through this class), their updated offset will not be reflected in this class'
     // animator so use this method to pull updated values when necessary.
     void updateScrollAnimator();
 
-    ScrollableArea& visualViewport() const { return m_visualViewport; }
-    ScrollableArea& layoutViewport() const { return m_layoutViewport; }
+    ScrollableArea& visualViewport() const { ASSERT(m_visualViewport); return *m_visualViewport; }
+    ScrollableArea& layoutViewport() const { ASSERT(m_layoutViewport); return *m_layoutViewport; }
 
-    ScrollableArea& m_visualViewport;
-    ScrollableArea& m_layoutViewport;
+    RawPtrWillBeMember<ScrollableArea> m_visualViewport;
+    RawPtrWillBeMember<ScrollableArea> m_layoutViewport;
 };
 
 } // namespace blink
 
 #endif // RootFrameViewport_h