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

third_party/WebKit/public/platform/WebThemeEngine.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 15 matching lines @@
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef WebThemeEngine_h
 #define WebThemeEngine_h
 
 #include "WebCanvas.h"
 #include "WebColor.h"
+#include "WebRect.h"
 #include "WebScrollbarOverlayColorTheme.h"
 #include "WebSize.h"
 
 namespace blink {
 
-struct WebRect;
-
 class WebThemeEngine {
  public:
   // The current state of the associated Part.
   enum State {
     StateDisabled,
     StateHover,
     StateNormal,
     StatePressed,
     StateFocused,
     StateReadonly,
@@ skipping 99 matching lines @@
     InnerSpinButtonExtraParams innerSpin;
     ProgressBarExtraParams progressBar;
     ScrollbarThumbExtraParams scrollbarThumb;
   };
 
   // Gets the size of the given theme part. For variable sized items
   // like vertical scrollbar thumbs, the width will be the required width of
   // the track while the height will be the minimum height.
   virtual WebSize getSize(Part) { return WebSize(); }
 
+  virtual bool supportsNinePatch(Part) const { return false; }
+  virtual WebSize ninePatchCanvasSize(Part) const { return WebSize(); }
+  virtual WebRect ninePatchAperture(Part) const { return WebRect(); }
+
   struct ScrollbarStyle {
     int thumbThickness;
     int scrollbarMargin;
     WebColor color;
     double fadeOutDelaySeconds;
     double fadeOutDurationSeconds;
   };
 
   // Gets the overlay scrollbar style. Not used on Mac.
   virtual void getOverlayScrollbarStyle(ScrollbarStyle* style) {
@@ skipping 11 matching lines @@
   virtual void paint(WebCanvas*,
                      Part,
                      State,
                      const WebRect&,
                      const ExtraParams*) {}
 };
 
 }  // namespace blink
 
 #endif