Draw main frame custom scrollbars in root layer scrolling mode.

third_party/WebKit/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 CompositedLayerMapping;
 class FrameView;
 class LayoutRect;
+class LocalFrame;
 
 // 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.
@@ skipping 45 matching lines @@
     IntSize contentsSize() const override;
     bool scrollbarsCanBeActive() const override;
     IntRect scrollableAreaBoundingBox() const override;
     bool userInputScrollable(ScrollbarOrientation) const override;
     bool shouldPlaceVerticalScrollbarOnLeft() const override;
     void scrollControlWasSetNeedsPaintInvalidation() override;
     GraphicsLayer* layerForContainer() const override;
     GraphicsLayer* layerForScrolling() const override;
     GraphicsLayer* layerForHorizontalScrollbar() const override;
     GraphicsLayer* layerForVerticalScrollbar() const override;
+    GraphicsLayer* layerForScrollCorner() const override;
     ScrollResult userScroll(ScrollGranularity, const FloatSize&) override;
     bool scrollAnimatorEnabled() const override;
     HostWindow* getHostWindow() const override;
     void serviceScrollAnimations(double) override;
     void updateCompositorScrollAnimations() override;
     void cancelProgrammaticScrollAnimation() override;
     ScrollBehavior scrollBehaviorStyle() const override;
     Widget* getWidget() override;
     void clearScrollAnimators() override;
     LayoutBox* layoutBox() const override;
 
 private:
     RootFrameViewport(ScrollableArea& visualViewport, ScrollableArea& layoutViewport);
 
     enum ViewportToScrollFirst {
         VisualViewport,
         LayoutViewport
     };
 
     DoublePoint scrollOffsetFromScrollAnimators() const;
 
     void distributeScrollBetweenViewports(const DoublePoint&, ScrollType, ScrollBehavior, ViewportToScrollFirst);
 
+    LocalFrame* mainFrame() const;
+    CompositedLayerMapping* compositedLayerMapping() 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 { ASSERT(m_visualViewport); return *m_visualViewport; }
 
     Member<ScrollableArea> m_visualViewport;
     Member<ScrollableArea> m_layoutViewport;
 };
 
 DEFINE_TYPE_CASTS(RootFrameViewport, ScrollableArea, scrollableArea, scrollableArea->isRootFrameViewport(), scrollableArea.isRootFrameViewport());
 
 } // namespace blink
 
 #endif // RootFrameViewport_h