Makes ash/wm/common a library

ash/wm/common/root_window_finder.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/wm/common/root_window_finder.h"
 
+#include "ash/wm/common/wm_lookup.h"
 #include "ash/wm/common/wm_root_window_controller.h"
 #include "ash/wm/common/wm_window.h"
 #include "ui/display/display.h"
 #include "ui/display/screen.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace ash {
 namespace wm {
 
 WmWindow* GetRootWindowAt(const gfx::Point& point) {
   const display::Display& display =
       display::Screen::GetScreen()->GetDisplayNearestPoint(point);
   DCHECK(display.is_valid());
   WmRootWindowController* root_window_controller =
-      WmRootWindowController::GetWithDisplayId(display.id());
+      WmLookup::Get()->GetRootWindowControllerWithDisplayId(display.id());
   return root_window_controller ? root_window_controller->GetWindow() : nullptr;
 }
 
 WmWindow* GetRootWindowMatching(const gfx::Rect& rect) {
   const display::Display& display =
       display::Screen::GetScreen()->GetDisplayMatching(rect);
   WmRootWindowController* root_window_controller =
-      WmRootWindowController::GetWithDisplayId(display.id());
+      WmLookup::Get()->GetRootWindowControllerWithDisplayId(display.id());
   return root_window_controller ? root_window_controller->GetWindow() : nullptr;
 }
 
 }  // namespace wm
 }  // namespace ash