cc: Don't pass simple well-defined classes by reference.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 3f1c322051dc2afc18e8df8d822d0abe908a1cc8..c7bbcc9dbe59fc1ac17c1b2bb16fc327915c5e79 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -93,7 +93,7 @@ void PictureLayerImpl::PushPropertiesTo(LayerImpl* base_layer) {
 
 void PictureLayerImpl::AppendQuads(QuadSink* quad_sink,
                                    AppendQuadsData* append_quads_data) {
-  const gfx::Rect& rect = visible_content_rect();
+  gfx::Rect rect(visible_content_rect());
   gfx::Rect content_rect(content_bounds());
 
   SharedQuadState* shared_quad_state =
@@ -540,7 +540,7 @@ bool PictureLayerImpl::AreVisibleResourcesReady() const {
   DCHECK(layer_tree_impl()->IsPendingTree());
   DCHECK(ideal_contents_scale_);
 
-  const gfx::Rect& rect = visible_content_rect();
+  gfx::Rect rect(visible_content_rect());
 
   float min_acceptable_scale =
       std::min(raster_contents_scale_, ideal_contents_scale_);