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

cc/blink/scrollbar_impl.cc

Index: cc/blink/scrollbar_impl.cc
diff --git a/cc/blink/scrollbar_impl.cc b/cc/blink/scrollbar_impl.cc
index 5df7cfe45ec67f474839eed124a7e5537ae131ab..9043eb276d6dca6fe38c2470ab8087718e82af4f 100644
--- a/cc/blink/scrollbar_impl.cc
+++ b/cc/blink/scrollbar_impl.cc
@@ -73,6 +73,18 @@ bool ScrollbarImpl::NeedsPaintPart(cc::ScrollbarPart part) const {
   return painter_.trackNeedsRepaint();
 }
 
+bool ScrollbarImpl::UsesNinePatchThumbResource() const {
+  return painter_.usesNinePatchThumbResource();
+}
+
+gfx::Size ScrollbarImpl::NinePatchThumbCanvasSize() const {
+  return geometry_->ninePatchThumbCanvasSize(scrollbar_.get());
+}
+
+gfx::Rect ScrollbarImpl::NinePatchThumbAperture() const {
+  return geometry_->ninePatchThumbAperture(scrollbar_.get());
+}
+
 void ScrollbarImpl::PaintPart(SkCanvas* canvas,
                               cc::ScrollbarPart part,
                               const gfx::Rect& content_rect) {