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

cc/trees/tree_synchronizer.cc

Index: cc/trees/tree_synchronizer.cc
diff --git a/cc/trees/tree_synchronizer.cc b/cc/trees/tree_synchronizer.cc
index 60177bf0648e7e0255e79d1b145740f023ceeb3d..6314afbae0ab754c5d26f1a837ff9eb789c6935e 100644
--- a/cc/trees/tree_synchronizer.cc
+++ b/cc/trees/tree_synchronizer.cc
@@ -13,6 +13,7 @@
 #include "cc/layers/layer.h"
 #include "cc/layers/layer_collections.h"
 #include "cc/layers/layer_impl.h"
+#include "cc/trees/layer_tree.h"
 #include "cc/trees/layer_tree_host.h"
 #include "cc/trees/layer_tree_impl.h"
 
@@ -104,7 +105,7 @@ void TreeSynchronizer::PushLayerProperties(LayerTreeImpl* pending_tree,
                               active_tree);
 }
 
-void TreeSynchronizer::PushLayerProperties(LayerTreeHost* host_tree,
+void TreeSynchronizer::PushLayerProperties(LayerTree* host_tree,
                                            LayerTreeImpl* impl_tree) {
   PushLayerPropertiesInternal(host_tree->LayersThatShouldPushProperties(),
                               impl_tree);