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

cc/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 component("cc") {
   sources = [
     "animation/animation.cc",
@@ skipping 479 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 527 matching lines @@
     "//ui/gfx/geometry",
     "//ui/gl",
     "//ui/gl:test_support",
   ]
 
   # This target should not require the Chrome executable to run.
   assert_no_deps = [ "//chrome" ]
 }
 # When adding support for isolates, please have a look at run-time dependencies
 # in the cc_unittests_run target in cc_tests.gyp.