Adds WmWindow and converts WindowState to use it

ash/wm/drag_details.h

Index: ash/wm/drag_details.h
diff --git a/ash/wm/drag_details.h b/ash/wm/drag_details.h
index c1554bbd2faf0faa7e22b7cbd5a118adec7ad5d2..60e6d1160466413ba3db6048953382c9226cf9cf 100644
--- a/ash/wm/drag_details.h
+++ b/ash/wm/drag_details.h
@@ -17,13 +17,15 @@ class Window;
 namespace ash {
 
 namespace wm {
+class WmWindow;
 class WindowState;
 }
 
 struct ASH_EXPORT DragDetails {
-  DragDetails(aura::Window* window,
+  DragDetails(wm::WmWindow* window,
               const gfx::Point& location,
               int window_component,
+              // TODO(sky): make wm type.
               aura::client::WindowMoveSource source);
   ~DragDetails();