Setup LayerTree class, refactor 2 functions from LayerTreeHost to it.

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': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 536 matching lines @@
         'trees/clip_node.h',
         'trees/compositor_mode.h',
         'trees/damage_tracker.cc',
         'trees/damage_tracker.h',
         'trees/draw_property_utils.cc',
         'trees/draw_property_utils.h',
         'trees/effect_node.cc',
         'trees/effect_node.h',
         'trees/latency_info_swap_promise_monitor.cc',
         'trees/latency_info_swap_promise_monitor.h',
+        'trees/layer_tree.cc',
+        'trees/layer_tree.h',
         'trees/layer_tree_host.cc',
         'trees/layer_tree_host.h',
         'trees/layer_tree_host_client.h',
         'trees/layer_tree_host_common.cc',
         'trees/layer_tree_host_common.h',
         'trees/layer_tree_host_impl.cc',
         'trees/layer_tree_host_impl.h',
         'trees/layer_tree_host_single_thread_client.h',
         'trees/layer_tree_impl.cc',
         'trees/layer_tree_impl.h',
@@ skipping 145 matching lines @@
         'surfaces/surface_resource_holder.h',
         'surfaces/surface_sequence.h',
         'surfaces/surfaces_export.h',
       ],
       'includes': [
         '../build/android/increase_size_for_speed.gypi',
       ],
     },
   ],
 }