Plumb PinchVirtualViewport layers into CC.

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index e362f84b4ca09789afc7c0ea734edab6f5039e9a..f85942785027ed673f998dda833f764eb895dc34 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -201,6 +201,11 @@ class CC_EXPORT LayerTreeHost : NON_EXPORTED_BASE(public RateLimiterClient) {
   void SetRootLayer(scoped_refptr<Layer> root_layer);
   Layer* root_layer() { return root_layer_.get(); }
   const Layer* root_layer() const { return root_layer_.get(); }
+  void RegisterPinchViewportLayers(
+      scoped_refptr<Layer> inner_viewport_clip_layer,
+      scoped_refptr<Layer> page_scale_layer,
+      scoped_refptr<Layer> inner_viewport_scroll_layer,
+      scoped_refptr<Layer> outer_viewport_scroll_layer);
 
   const LayerTreeSettings& settings() const { return settings_; }
 
@@ -418,6 +423,11 @@ class CC_EXPORT LayerTreeHost : NON_EXPORTED_BASE(public RateLimiterClient) {
   LCDTextMetrics lcd_text_metrics_;
   int tree_id_;
 
+  scoped_refptr<Layer> inner_viewport_clip_layer_;
+  scoped_refptr<Layer> page_scale_layer_;
+  scoped_refptr<Layer> inner_viewport_scroll_layer_;
+  scoped_refptr<Layer> outer_viewport_scroll_layer_;
+
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHost);
 };