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

cc/test/fake_scrollbar.cc

Index: cc/test/fake_scrollbar.cc
diff --git a/cc/test/fake_scrollbar.cc b/cc/test/fake_scrollbar.cc
index 7ddafd486ce56c8fafe9ba5cde2c45167f338989..57a6ceefa2de8404e55dd42a4d4dad6346891c01 100644
--- a/cc/test/fake_scrollbar.cc
+++ b/cc/test/fake_scrollbar.cc
@@ -91,4 +91,16 @@ void FakeScrollbar::PaintPart(PaintCanvas* canvas,
   canvas->drawRect(rect, flags);
 }
 
+bool FakeScrollbar::UsesNinePatchThumbResource() const {
+  return false;
+}
+
+gfx::Size FakeScrollbar::NinePatchThumbCanvasSize() const {
+  return gfx::Size();
+}
+
+gfx::Rect FakeScrollbar::NinePatchThumbAperture() const {
+  return gfx::Rect();
+}
+
 }  // namespace cc