Add support for (de)serializing HeadsUpDisplayLayer

cc/trees/layer_tree_host_unittest_serialization.cc

 // Copyright 2015 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/trees/layer_tree_host.h"
 
 #include "cc/layers/heads_up_display_layer.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/layer_settings.h"
 #include "cc/proto/layer.pb.h"
@@ skipping 89 matching lines @@
               layer_tree_host_dst_->has_transparent_background_);
     EXPECT_EQ(layer_tree_host_src_->in_paint_layer_contents_,
               layer_tree_host_dst_->in_paint_layer_contents_);
     EXPECT_EQ(layer_tree_host_src_->id_, layer_tree_host_dst_->id_);
     EXPECT_EQ(layer_tree_host_src_->next_commit_forces_redraw_,
               layer_tree_host_dst_->next_commit_forces_redraw_);
 
     if (layer_tree_host_src_->hud_layer_) {
       EXPECT_EQ(layer_tree_host_src_->hud_layer_->id(),
                 layer_tree_host_dst_->hud_layer_->id());
+      // The HUD layer member is a HeadsUpDisplayLayer instead of Layer, so
+      // inspect the proto to see if it contains the the right layer type.
+      bool found_hud_layer_type = false;
+      for (int i = 0; i < proto.root_layer().children_size(); ++i) {
+        if (proto.root_layer().children(i).id() ==
+            layer_tree_host_src_->hud_layer_->id()) {
+          EXPECT_EQ(proto::HEADS_UP_DISPLAY_LAYER,
+                    proto.root_layer().children(i).type());
+          found_hud_layer_type = true;
+          break;
+        }
+      }
+      EXPECT_TRUE(found_hud_layer_type);
     } else {
       EXPECT_EQ(nullptr, layer_tree_host_dst_->hud_layer_);
     }
     if (layer_tree_host_src_->overscroll_elasticity_layer_) {
       EXPECT_EQ(layer_tree_host_src_->overscroll_elasticity_layer_->id(),
                 layer_tree_host_dst_->overscroll_elasticity_layer_->id());
     } else {
       EXPECT_EQ(nullptr, layer_tree_host_dst_->overscroll_elasticity_layer_);
     }
     if (layer_tree_host_src_->page_scale_layer_) {
@@ skipping 184 matching lines @@
 
 TEST_F(LayerTreeHostSerializationTest, LayersChanged) {
   RunLayersChangedTest();
 }
 
 TEST_F(LayerTreeHostSerializationTest, LayersChangedMultipleSerializations) {
   LayersChangedMultipleSerializations();
 }
 
 }  // namespace cc