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

cc/blink/web_scrollbar_layer_impl.h

Index: cc/blink/web_scrollbar_layer_impl.h
diff --git a/cc/blink/web_scrollbar_layer_impl.h b/cc/blink/web_scrollbar_layer_impl.h
index 3fd192efe843a23ffd95256e4858bdc4c6deac55..ad203e9a9563e115e5779e865f57aa07fb3bc700 100644
--- a/cc/blink/web_scrollbar_layer_impl.h
+++ b/cc/blink/web_scrollbar_layer_impl.h
@@ -28,6 +28,11 @@ class WebScrollbarLayerImpl : public blink::WebScrollbarLayer {
       blink::WebScrollbarThemePainter painter,
       std::unique_ptr<blink::WebScrollbarThemeGeometry> geometry);
   CC_BLINK_EXPORT WebScrollbarLayerImpl(
+      std::unique_ptr<blink::WebScrollbar> scrollbar,
+      blink::WebScrollbarThemePainter painter,
+      std::unique_ptr<blink::WebScrollbarThemeGeometry> geometry,
+      bool temp);
+  CC_BLINK_EXPORT WebScrollbarLayerImpl(
       blink::WebScrollbar::Orientation orientation,
       int thumb_thickness,
       int track_start,