cc: Early-out UpdateTilePriorities if the layer has no tilings

R=enne
BUG=176312
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/14378007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@195369 0039d316-1c4b-4281-b951-d872f2087c98

cc/layers/picture_layer_impl.cc

@@ -262,6 +262,9 @@ void PictureLayerImpl::DumpLayerProperties(std::string*, int indent) const {
 }
 
 void PictureLayerImpl::UpdateTilePriorities() {
+  if (!tilings_->num_tilings())
+    return;
+
   UpdateLCDTextStatus();
 
   int current_source_frame_number = layer_tree_impl()->source_frame_number();