Adds WmWindow and converts WindowState to use it

ash/wm/window_resizer.h

Index: ash/wm/window_resizer.h
diff --git a/ash/wm/window_resizer.h b/ash/wm/window_resizer.h
index 2c8f8a4c3247149c6e02d56fd1afb6ee9c31286f..af7a92c558fcbeddcac9dc083f13bfbb3e50b205 100644
--- a/ash/wm/window_resizer.h
+++ b/ash/wm/window_resizer.h
@@ -57,7 +57,7 @@ class ASH_EXPORT WindowResizer {
 
   // Returns the target window the resizer was created for.
   aura::Window* GetTarget() const {
-    return window_state_ ? window_state_->window() : NULL;
+    return window_state_ ? window_state_->aura_window() : NULL;
   }
 
   // See comment for |DragDetails::initial_location_in_parent|.
@@ -99,6 +99,7 @@ class ASH_EXPORT WindowResizer {
 
 // Creates a WindowResizer for |window|. This can return a scoped_ptr
 // initialized with NULL if |window| should not be resized nor dragged.
+// TODO(sky): move this to its own file. This is aura specific.
 ASH_EXPORT std::unique_ptr<WindowResizer> CreateWindowResizer(
     aura::Window* window,
     const gfx::Point& point_in_parent,