Implement Sebastien's overlay scrollbars for native UI (Views).

ui/views/controls/scroll_view.h

 // Copyright (c) 2012 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 UI_VIEWS_CONTROLS_SCROLL_VIEW_H_
 #define UI_VIEWS_CONTROLS_SCROLL_VIEW_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
@@ skipping 79 matching lines @@
 
   // Sets whether this ScrollView has a focus ring or not.
   void SetHasFocusRing(bool has_focus_ring);
 
   // View overrides:
   gfx::Size GetPreferredSize() const override;
   int GetHeightForWidth(int width) const override;
   void Layout() override;
   bool OnKeyPressed(const ui::KeyEvent& event) override;
   bool OnMouseWheel(const ui::MouseWheelEvent& e) override;
-  void OnMouseEntered(const ui::MouseEvent& event) override;
-  void OnMouseExited(const ui::MouseEvent& event) override;
   void OnScrollEvent(ui::ScrollEvent* event) override;
   void OnGestureEvent(ui::GestureEvent* event) override;
   const char* GetClassName() const override;
 
   // ScrollBarController overrides:
   void ScrollToPosition(ScrollBar* source, int position) override;
   int GetScrollIncrement(ScrollBar* source,
                          bool is_page,
                          bool is_positive) override;
 
@@ skipping 148 matching lines @@
  private:
   int top_margin_;
   int row_height_;
 
   DISALLOW_COPY_AND_ASSIGN(FixedRowHeightScrollHelper);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_SCROLL_VIEW_H_