Make all gesture scrolls use customization path internally

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"
 
@@ skipping 32 matching lines @@
     // will ensure that the effectiveRootScroller element always has this set as
     // the apply scroll callback.
     static RootScrollerController* create(
         Document& document,
         ViewportScrollCallback* applyScrollCallback)
     {
         return new RootScrollerController(document, applyScrollCallback);
     }
 
     // Creates an apply scroll callback that handles viewport actions like
-    // TopControls movement and Overscroll.
+    // TopControls movement and Overscroll. The TopControls and
+    // OverscrollController are given to the ViewportScrollCallback but are not
+    // owned or kept alive by it.
     static ViewportScrollCallback* createViewportApplyScroll(
-        TopControls&, OverscrollController&);
+        TopControls*, OverscrollController*);
 
     DECLARE_TRACE();
 
     // Sets the element that will be used as the root scroller. This can be
     // nullptr, in which case we'll use the default element (documentElement) as
     // the effective root scroller.
     void set(Element*);
 
     // Returns the element currently set as the root scroller from script. This
     // differs from the effective root scroller since the set Element may not
     // currently be a valid root scroller. e.g. If the page sets an Element
     // with `display: none`, get() will return that element, even though the
     // effective root scroller will remain the element returned by
     // defaultEffectiveRootScroller().
     Element* get() const;
 
     // 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 defualt root scroller.
     void didUpdateLayout();
 
+    // TODO(bokan): Temporarily exposed to allow ScrollCustomization to
+    // differentiate between real custom callback and the built-in viewport
+    // apply scroll.
+    const ViewportScrollCallback* viewportScrollCallback()
+    {
+        return m_viewportApplyScroll;
+    }
+
 private:
     RootScrollerController(Document&, ViewportScrollCallback*);
 
     Element* defaultEffectiveRootScroller();
 
     // Ensures the effective root scroller is currently valid and replaces it
     // with the default if not.
     void updateEffectiveRootScroller();
     void moveViewportApplyScroll(Element* target);
 
     WeakMember<Document> m_document;
     Member<ViewportScrollCallback> m_viewportApplyScroll;
 
     WeakMember<Element> m_rootScroller;
     WeakMember<Element> m_effectiveRootScroller;
 };
 
 } // namespace blink
 
 #endif // RootScrollerController_h