Turn off computation of the interest rect in cc in synchronized paint mode.

cc/layers/content_layer_client.h

Index: cc/layers/content_layer_client.h
diff --git a/cc/layers/content_layer_client.h b/cc/layers/content_layer_client.h
index d56ab6e2c8e8940d8d0e28c96592caf55a33f88b..470fb22f892adbf35d052c85f1ee253a0f326e90 100644
--- a/cc/layers/content_layer_client.h
+++ b/cc/layers/content_layer_client.h
@@ -23,9 +23,15 @@ class CC_EXPORT ContentLayerClient {
     DISPLAY_LIST_PAINTING_DISABLED
   };
 
+  // The |recording_viewport| rect defines the region of interest.
+  // |recording_viewport| may be set by the callee to a different value.
+  // The resulting WebDisplayItemList should contain sufficient content to
+  // correctly paint the final value of |recording_viewport|, but may also
+  // contain other content. The result will be clipped on playback to the
+  // final value of |recording_viewport|.
   virtual scoped_refptr<DisplayItemList> PaintContentsToDisplayList(
-      const gfx::Rect& clip,
-      PaintingControlSetting painting_status) = 0;
+      PaintingControlSetting painting_status,
+      gfx::Rect* recording_viewport) = 0;
 
   // If true the layer may skip clearing the background before rasterizing,
   // because it will cover any uncleared data with content.