Disable clipping on root scroller's ancestors.

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 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 56 matching lines @@
     // element.
     virtual GraphicsLayer* rootScrollerLayer();
 
     // Returns true if the given ScrollStateCallback is the
     // ViewportScrollCallback managed by this class.
     // TODO(bokan): Temporarily needed to allow ScrollCustomization to
     // differentiate between real custom callback and the built-in viewport
     // apply scroll. crbug.com/623079.
     virtual bool isViewportScrollCallback(const ScrollStateCallback*) const;
 
+    PaintLayer* rootScrollerPaintLayer() const;
+
 protected:
     RootScrollerController(Document&);
 
     // Called when the root scroller of any descendant frames changes. This
     // will only ever be called on the top document's RootScrollerController.
     virtual void globalRootScrollerMayHaveChanged();
 
     // Returns the ScrollableArea to use to scroll the given Element.
     ScrollableArea* scrollableAreaFor(const Element&) const;
 
@@ skipping 22 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