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

cc/test/fake_layer_tree_host.cc

Index: cc/test/fake_layer_tree_host.cc
diff --git a/cc/test/fake_layer_tree_host.cc b/cc/test/fake_layer_tree_host.cc
index 4d214fb9f535a4c73146ff5c2655397855f9ba1d..b112f13bd3db780439bddfaae22eb6b014ef42ae 100644
--- a/cc/test/fake_layer_tree_host.cc
+++ b/cc/test/fake_layer_tree_host.cc
@@ -87,8 +87,8 @@ void FakeLayerTreeHost::SetNeedsCommit() { needs_commit_ = true; }
 LayerImpl* FakeLayerTreeHost::CommitAndCreateLayerImplTree() {
   TreeSynchronizer::SynchronizeTrees(root_layer(), active_tree());
   active_tree()->SetPropertyTrees(property_trees());
-  TreeSynchronizer::PushLayerProperties(root_layer()->layer_tree_host(),
-                                        active_tree());
+  TreeSynchronizer::PushLayerProperties(
+      root_layer()->layer_tree_host()->GetLayerTree(), active_tree());
   animation_host()->PushPropertiesTo(host_impl_.animation_host());
 
   active_tree()->UpdatePropertyTreeScrollOffset(property_trees());
@@ -109,8 +109,8 @@ LayerImpl* FakeLayerTreeHost::CommitAndCreateLayerImplTree() {
 LayerImpl* FakeLayerTreeHost::CommitAndCreatePendingTree() {
   TreeSynchronizer::SynchronizeTrees(root_layer(), pending_tree());
   pending_tree()->SetPropertyTrees(property_trees());
-  TreeSynchronizer::PushLayerProperties(root_layer()->layer_tree_host(),
-                                        pending_tree());
+  TreeSynchronizer::PushLayerProperties(
+      root_layer()->layer_tree_host()->GetLayerTree(), pending_tree());
   animation_host()->PushPropertiesTo(host_impl_.animation_host());
 
   pending_tree()->UpdatePropertyTreeScrollOffset(property_trees());