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

cc/blink/web_content_layer_impl.cc

Index: cc/blink/web_content_layer_impl.cc
diff --git a/cc/blink/web_content_layer_impl.cc b/cc/blink/web_content_layer_impl.cc
index 2990978df6f91ebea23efdae83beea7f603a2278..174054d5ba125b37b137f513dc4e09d4f01ca032 100644
--- a/cc/blink/web_content_layer_impl.cc
+++ b/cc/blink/web_content_layer_impl.cc
@@ -58,6 +58,10 @@ blink::WebLayer* WebContentLayerImpl::layer() {
   return layer_.get();
 }
 
+gfx::Rect WebContentLayerImpl::PaintableRegion() {
+  return client_->paintableRegion();
+}
+
 scoped_refptr<cc::DisplayItemList>
 WebContentLayerImpl::PaintContentsToDisplayList(
     const gfx::Rect& clip,