cc: Simplify the logic for deciding to update tile priorities.

cc/picture_layer_impl.cc

Index: cc/picture_layer_impl.cc
diff --git a/cc/picture_layer_impl.cc b/cc/picture_layer_impl.cc
index fc0e9d0952ba72ff45a05da559b6c6cb73c815de..85447ad172d0dad23aa0ebdb9c0e95f7764b9f4e 100644
--- a/cc/picture_layer_impl.cc
+++ b/cc/picture_layer_impl.cc
@@ -216,6 +216,14 @@ void PictureLayerImpl::dumpLayerProperties(std::string*, int indent) const {
 }
 
 void PictureLayerImpl::updateTilePriorities() {
+  if (!tilings_->num_tilings()) {
+    last_screen_space_transform_ = screenSpaceTransform();
+    last_bounds_ = bounds();
+    last_content_bounds_ = contentBounds();
+    last_content_scale_ = contentsScaleX();
+    return;
+  }
+
   int current_source_frame_number = layerTreeImpl()->source_frame_number();
   double current_frame_time =
       (layerTreeImpl()->CurrentFrameTime() - base::TimeTicks()).InSecondsF();