chromeos: removes WmWindow usage from MultiWindowResizeController

ash/root_window_controller.h

Index: ash/root_window_controller.h
diff --git a/ash/root_window_controller.h b/ash/root_window_controller.h
index 493e9d94f63c0a8afe86fb67086532a0c6cc63c2..265ebcccb0049ab4fc2079d1d99422a53cf3243f 100644
--- a/ash/root_window_controller.h
+++ b/ash/root_window_controller.h
@@ -199,7 +199,7 @@ class ASH_EXPORT RootWindowController : public ShellObserver {
   //
   // NOTE: the returned window may not contain the location as resize handles
   // may extend outside the bounds of the window.
-  WmWindow* FindEventTarget(const gfx::Point& location_in_screen);
+  aura::Window* FindEventTarget(const gfx::Point& location_in_screen);
 
   // Gets the last location seen in a mouse event in this root window's
   // coordinates. This may return a point outside the root window's bounds.