cc: Make PaintedScrollbarLayer not use ContentsScalingLayer

cc/layers/painted_scrollbar_layer_impl.h

Index: cc/layers/painted_scrollbar_layer_impl.h
diff --git a/cc/layers/painted_scrollbar_layer_impl.h b/cc/layers/painted_scrollbar_layer_impl.h
index 8708b748662b0a7cdeefcbffa38310c8f4c3b97d..131576ba471be82a430f263e52dc7dc230d4cf2b 100644
--- a/cc/layers/painted_scrollbar_layer_impl.h
+++ b/cc/layers/painted_scrollbar_layer_impl.h
@@ -45,10 +45,11 @@ class CC_EXPORT PaintedScrollbarLayerImpl : public ScrollbarLayerImplBase {
     thumb_ui_resource_id_ = uid;
   }
 
- protected:
-  PaintedScrollbarLayerImpl(LayerTreeImpl* tree_impl,
-                            int id,
-                            ScrollbarOrientation orientation);
+  void set_internal_content_scale_and_bounds(float content_scale,
+                                             const gfx::Size& content_bounds) {
+    internal_content_scale_ = content_scale;
+    internal_content_bounds_ = content_bounds;
+  }
 
   // ScrollbarLayerImplBase implementation.
   int ThumbThickness() const override;
@@ -56,6 +57,12 @@ class CC_EXPORT PaintedScrollbarLayerImpl : public ScrollbarLayerImplBase {
   float TrackLength() const override;
   int TrackStart() const override;
   bool IsThumbResizable() const override;
+  gfx::Rect ComputeThumbQuadRect() const override;
+
+ protected:
+  PaintedScrollbarLayerImpl(LayerTreeImpl* tree_impl,
+                            int id,
+                            ScrollbarOrientation orientation);
 
  private:
   const char* LayerTypeAsString() const override;
@@ -63,6 +70,9 @@ class CC_EXPORT PaintedScrollbarLayerImpl : public ScrollbarLayerImplBase {
   UIResourceId track_ui_resource_id_;
   UIResourceId thumb_ui_resource_id_;
 
+  float internal_content_scale_;
+  gfx::Size internal_content_bounds_;
+
   int thumb_thickness_;
   int thumb_length_;
   int track_start_;