Enable more layer_tree_host_unittest for LayerTreeHostRemote.

cc/blimp/layer_tree_host_remote.cc

Index: cc/blimp/layer_tree_host_remote.cc
diff --git a/cc/blimp/layer_tree_host_remote.cc b/cc/blimp/layer_tree_host_remote.cc
index b5d129f98fa96827229497c63be9b1e9ae1afbf5..b71d843f6aa7937a87bc202b44fdcdec2e557f0d 100644
--- a/cc/blimp/layer_tree_host_remote.cc
+++ b/cc/blimp/layer_tree_host_remote.cc
@@ -488,10 +488,13 @@ void LayerTreeHostRemote::SerializeCurrentState(
                           inputs_only);
 
   // Serialize the dirty layers.
-  for (auto* layer : layer_tree_->LayersThatShouldPushProperties())
+  std::unordered_set<Layer*> layers_need_push_properties;
+  layers_need_push_properties.swap(
+      layer_tree_->LayersThatShouldPushProperties());
+
+  for (auto* layer : layers_need_push_properties)
     layer->ToLayerPropertiesProto(
         layer_tree_host_proto->mutable_layer_updates(), inputs_only);
-  layer_tree_->LayersThatShouldPushProperties().clear();
 
   std::vector<PictureData> pictures =
       engine_picture_cache_->CalculateCacheUpdateAndFlush();