Move LayerSorter to exist locally only in layer_tree_host_common

cc/layer_tree_host_impl.h

Index: cc/layer_tree_host_impl.h
diff --git a/cc/layer_tree_host_impl.h b/cc/layer_tree_host_impl.h
index 675d765fb8b9b4e792822752bdfb3573f2d70b7c..cc1289947233d06af892b3a3e89d4b2289702108 100644
--- a/cc/layer_tree_host_impl.h
+++ b/cc/layer_tree_host_impl.h
@@ -11,7 +11,6 @@
 #include "cc/animation_events.h"
 #include "cc/cc_export.h"
 #include "cc/input_handler.h"
-#include "cc/layer_sorter.h"
 #include "cc/render_pass.h"
 #include "cc/render_pass_sink.h"
 #include "cc/renderer.h"
@@ -365,8 +364,6 @@ private:
     // This is used for ticking animations slowly when hidden.
     scoped_ptr<LayerTreeHostImplTimeSourceAdapter> m_timeSourceClientAdapter;
 
-    LayerSorter m_layerSorter;
-
     // List of visible layers for the most recently prepared frame. Used for
     // rendering and input event hit testing.
     LayerList m_renderSurfaceLayerList;