Fix scrollbar buttons on ChromeOS.

ui/native_theme/native_theme.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_NATIVE_THEME_NATIVE_THEME_H_
 #define UI_NATIVE_THEME_NATIVE_THEME_H_
 
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "build/build_config.h"
@@ skipping 203 matching lines @@
     SliderExtraParams slider;
     TextFieldExtraParams text_field;
     TrackbarExtraParams trackbar;
   };
 
   // Return the size of the part.
   virtual gfx::Size GetPartSize(Part part,
                                 State state,
                                 const ExtraParams& extra) const = 0;
 
+  virtual bool HasScrollbarButtons() const;
+
   // Paint the part to the canvas.
   virtual void Paint(SkCanvas* canvas,
                      Part part,
                      State state,
                      const gfx::Rect& rect,
                      const ExtraParams& extra) const = 0;
 
   // Paint part during state transition, used for overlay scrollbar state
   // transition animation.
   virtual void PaintStateTransition(SkCanvas* canvas,
@@ skipping 144 matching lines @@
  private:
   // Observers to notify when the native theme changes.
   base::ObserverList<NativeThemeObserver> native_theme_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeTheme);
 };
 
 }  // namespace ui
 
 #endif  // UI_NATIVE_THEME_NATIVE_THEME_H_