Use nine-patch resource for drawing Aura overlay scrollbar thumb.

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"
 #include "third_party/skia/include/core/SkColor.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/geometry/size.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/native_theme/native_theme_export.h"
 
 class SkCanvas;
 
-namespace gfx {
-class Rect;
-class Size;
-}
-
 namespace ui {
 
 class NativeThemeObserver;
 
 // This class supports drawing UI controls (like buttons, text fields, lists,
 // comboboxes, etc) that look like the native UI controls of the underlying
 // platform, such as Windows or Linux. It also supplies default colors for
 // dialog box backgrounds, etc., which are obtained from the system theme where
 // possible.
 //
@@ skipping 195 matching lines @@
                                 State state,
                                 const ExtraParams& extra) const = 0;
 
   // 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,
-                                    Part part,
-                                    State startState,
-                                    State endState,
-                                    double progress,
-                                    const gfx::Rect& rect,
-                                    ScrollbarOverlayColorTheme theme) const {}
+  virtual bool SupportsNinePatch(Part part) const = 0;
+  virtual gfx::Size GetNinePatchCanvasSize(Part part) const = 0;
+  virtual gfx::Rect GetNinePatchAperture(Part part) const = 0;
 
   // Supports theme specific colors.
   void SetScrollbarColors(unsigned inactive_color,
                           unsigned active_color,
                           unsigned track_color);
 
   // Colors for GetSystemColor().
   enum ColorId {
     // Windows
     kColorId_WindowBackground,
@@ skipping 131 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_