Add support for (de)serializing LayerTreeHost.

cc/cc_tests.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
     'cc_unit_tests_source_files': [
       'animation/animation_host_unittest.cc',
       'animation/animation_player_unittest.cc',
@@ skipping 126 matching lines @@
       'trees/layer_tree_host_unittest_animation_timelines.cc',
       'trees/layer_tree_host_unittest_context.cc',
       'trees/layer_tree_host_unittest_copyrequest.cc',
       'trees/layer_tree_host_unittest_damage.cc',
       'trees/layer_tree_host_unittest_delegated.cc',
       'trees/layer_tree_host_unittest_occlusion.cc',
       'trees/layer_tree_host_unittest_picture.cc',
       'trees/layer_tree_host_unittest_proxy.cc',
       'trees/layer_tree_host_unittest_record_gpu_histogram.cc',
       'trees/layer_tree_host_unittest_scroll.cc',
+      'trees/layer_tree_host_unittest_serialization.cc',
       'trees/layer_tree_host_unittest_video.cc',
       'trees/layer_tree_impl_unittest.cc',
       'trees/layer_tree_settings_unittest.cc',
       'trees/occlusion_tracker_unittest.cc',
       'trees/occlusion_unittest.cc',
       'trees/property_tree_unittest.cc',
       'trees/threaded_channel_unittest.cc',
       'trees/tree_synchronizer_unittest.cc',
     ],
     'cc_surfaces_unit_tests_source_files': [
@@ skipping 337 matching lines @@
                   '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
                 ],
               }
             ],
           ],
         },
       ],
     }],
   ],
 }