Detach PaintLayerScrollableArea from RootFrameViewport when disposed.

third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h

 // Copyright 2016 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 RootScrollerController_h
 #define RootScrollerController_h
 
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class Document;
 class Element;
 class GraphicsLayer;
 class PaintLayer;
+class PaintLayerScrollableArea;
 class ScrollableArea;
 class ScrollStateCallback;
 
 // Manages the root scroller associated with a given document. The root
 // scroller causes top controls movement, overscroll effects and prevents
 // chaining scrolls up further in the DOM. It can be set from script using
 // document.setRootScroller.
 //
 // There are two notions of a root scroller in this class: m_rootScroller and
 // m_effectiveRootScroller. The former is the Element that was set as the root
@@ skipping 36 matching lines @@
     // This returns the Element that's actually being used to control viewport
     // actions right now. This is different from get() if a root scroller hasn't
     // been set, or if the set root scroller isn't currently a valid scroller.
     Element* effectiveRootScroller() const;
 
     // This class needs to be informed of changes in layout so that it can
     // determine if the current root scroller is still valid or if it must be
     // replaced by the default root scroller.
     void didUpdateLayout();
 
+    // PaintLayerScrollableAreas need to notify this class when they're being
+    // disposed so that we can remove them as the root scroller.
+    void didDisposePaintLayerScrollableArea(PaintLayerScrollableArea&);
+
     // Returns the PaintLayer associated with the currently effective root
     // scroller.
     PaintLayer* rootScrollerPaintLayer() const;
 
 private:
     RootScrollerController(Document&);
 
     // Ensures the effective root scroller is currently valid and replaces it
     // with the default if not.
     void recomputeEffectiveRootScroller();
@@ skipping 17 matching lines @@
 
     // The element currently being used as the root scroller in this Document.
     // If the m_rootScroller is valid this will point to it. Otherwise, it'll
     // use a default Element.
     WeakMember<Element> m_effectiveRootScroller;
 };
 
 } // namespace blink
 
 #endif // RootScrollerController_h