cc: Throttle tile priority updates to once a frame.

cc/layer_tree_impl.h

Index: cc/layer_tree_impl.h
diff --git a/cc/layer_tree_impl.h b/cc/layer_tree_impl.h
index ac6065dfa2ec6054533a92cec246c3ec8ca9da29..8f3b36e296cd73f5c8c9dd731d9ed03e09f7a143 100644
--- a/cc/layer_tree_impl.h
+++ b/cc/layer_tree_impl.h
@@ -113,8 +113,14 @@ class CC_EXPORT LayerTreeImpl {
     has_transparent_background_ = transparent;
   }
 
+  enum UpdateDrawPropertiesReason {
+    UPDATE_PENDING_TREE,
+    UPDATE_ACTIVE_TREE,
+    UPDATE_ACTIVE_TREE_FOR_DRAW
+  };
+
   // Updates draw properties and render surface layer list
-  void UpdateDrawProperties();
+  void UpdateDrawProperties(UpdateDrawPropertiesReason reason);
   void set_needs_update_draw_properties() {
     needs_update_draw_properties_ = true;
   }