[cc] Move root layer pointer to LayerTreeImpl

cc/cc.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': {
     'cc_source_files': [
       'active_animation.cc',
       'active_animation.h',
       'animation_curve.cc',
@@ skipping 84 matching lines @@
       'layer_sorter.h',
       'layer_tiling_data.cc',
       'layer_tiling_data.h',
       'layer_tree_host.cc',
       'layer_tree_host.h',
       'layer_tree_host_client.h',
       'layer_tree_host_common.cc',
       'layer_tree_host_common.h',
       'layer_tree_host_impl.cc',
       'layer_tree_host_impl.h',
+      'layer_tree_impl.cc',
+      'layer_tree_impl.h',
       'layer_updater.cc',
       'layer_updater.h',
       'managed_memory_policy.cc',
       'managed_memory_policy.h',
       'math_util.cc',
       'math_util.h',
       'nine_patch_layer.cc',
       'nine_patch_layer.h',
       'nine_patch_layer_impl.cc',
       'nine_patch_layer_impl.h',
@@ skipping 178 matching lines @@
       ],
       'all_dependent_settings': {
         'include_dirs': [
           # Needed for <public/WebTransformationMatrix.h> in layer.h
           '<(webkit_src_dir)/Source/Platform/chromium',
         ],
       }
     },
   ],
 }