Make ViewportScrollCallback an interface and add child and root classes

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

Index: third_party/WebKit/Source/core/page/scrolling/RootViewportScrollCallback.h
diff --git a/third_party/WebKit/Source/core/page/scrolling/RootViewportScrollCallback.h b/third_party/WebKit/Source/core/page/scrolling/RootViewportScrollCallback.h
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index 0000000000000000000000000000000000000000..ea52090dc3149b4621b18dddf3eed8fb4c2cf55c
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+++ b/third_party/WebKit/Source/core/page/scrolling/RootViewportScrollCallback.h
@@ -0,0 +1,55 @@
+// 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 RootViewportScrollCallback_h
+#define RootViewportScrollCallback_h
+
+#include "core/page/scrolling/ViewportScrollCallback.h"
+#include "platform/heap/Handle.h"
+#include "platform/scroll/ScrollTypes.h"
+
+namespace blink {
+
+class FloatSize;
+class ScrollableArea;
+class ScrollState;
+class TopControls;
+class OverscrollController;
+
+// The ViewportScrollCallback used by the one root frame on the page. This
+// callback provides scrolling of the frame as well as associated actions like
+// top controls movement and overscroll glow.
+class RootViewportScrollCallback : public ViewportScrollCallback {
+public:
+    // The TopControls and OverscrollController are given to the
+    // RootViewportScrollCallback but are not owned or kept alive by it.
+    static RootViewportScrollCallback* create(
+        TopControls* topControls, OverscrollController* overscrollController)
+    {
+        return new RootViewportScrollCallback(topControls, overscrollController);
+    }
+
+    virtual ~RootViewportScrollCallback();
+
+    void handleEvent(ScrollState*) override;
+    void setScroller(ScrollableArea*) override;
+
+    DECLARE_VIRTUAL_TRACE();
+
+private:
+    // RootViewportScrollCallback does not assume ownership of TopControls or of
+    // OverscrollController.
+    RootViewportScrollCallback(TopControls*, OverscrollController*);
+
+    bool shouldScrollTopControls(const FloatSize&, ScrollGranularity) const;
+    bool scrollTopControls(ScrollState&);
+
+    WeakMember<TopControls> m_topControls;
+    WeakMember<OverscrollController> m_overscrollController;
+    WeakMember<ScrollableArea> m_scroller;
+};
+
+} // namespace blink
+
+#endif // RootViewportScrollCallback_h