Enable more layer_tree_host_unittest for LayerTreeHostRemote.

cc/blimp/layer_tree_host_remote.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/blimp/layer_tree_host_remote.h"
 
 #include "base/atomic_sequence_num.h"
 #include "base/auto_reset.h"
 #include "base/memory/ptr_util.h"
 #include "cc/animation/animation_host.h"
@@ skipping 469 matching lines @@
 void LayerTreeHostRemote::SerializeCurrentState(
     proto::LayerTreeHost* layer_tree_host_proto) {
   // We need to serialize only the inputs received from the embedder.
   const bool inputs_only = true;
 
   // Serialize the LayerTree.
   layer_tree_->ToProtobuf(layer_tree_host_proto->mutable_layer_tree(),
                           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());

[Khushal, 2016/10/28 23:11:50]

Do you mind adding a small test for this in layer_tree_host_remote_unittest?

Create a tree with 3 layers or so and in the first frame, all layers would be
serialized. Then modify a single layer and make sure in the second frame only
that layer is serialized?

[xingliu, 2016/10/31 18:48:05]

Done, make sense. Also tweak UpdateTrackingRemoteCompositorBridge in
layer_tree_host_remote_unittest.cc, not sure if this is really needed.

+
+  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();
   proto::PictureDataVectorToSkPicturesProto(
       pictures, layer_tree_host_proto->mutable_pictures());
 }
 
 }  // namespace cc