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 761586b116347417ddb6048a81d3f8495e377cf7..4ba11e33ee2343c71bfb223113495c95b65f6fe3 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(cc::PaintCanvas* canvas,
                               cc::ScrollbarPart part,
                               const gfx::Rect& content_rect) {