Moves couple of WmShell methods to standalone functions

ash/common/wm/fullscreen_window_finder.cc

 // Copyright 2016 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/common/wm/fullscreen_window_finder.h"
 
 #include "ash/common/wm/switchable_windows.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/common/wm_shell.h"

[James Cook, 2017/03/31 19:29:52]

nit: still needed?

[sky, 2017/03/31 20:15:14]

Done.

 #include "ash/common/wm_window.h"
 #include "ash/public/cpp/shell_window_ids.h"
+#include "ash/wm/window_util.h"
 #include "ui/compositor/layer.h"
 
 namespace ash {
 namespace wm {
 
 WmWindow* GetWindowForFullscreenMode(WmWindow* context) {
   WmWindow* topmost_window = nullptr;
-  WmWindow* active_window = context->GetShell()->GetActiveWindow();
+  WmWindow* active_window = WmWindow::Get(GetActiveWindow());
   if (active_window &&
       active_window->GetRootWindow() == context->GetRootWindow() &&
       IsSwitchableContainer(active_window->GetParent())) {
     // Use the active window when it is on the current root window to determine
     // the fullscreen state to allow temporarily using a panel (which is always
     // above the default container) while a fullscreen window is open. We only
     // use the active window when in a switchable container as the launcher
     // should not exit fullscreen mode.
     topmost_window = active_window;
   } else {
@@ skipping 14 matching lines @@
   while (topmost_window) {
     if (topmost_window->GetWindowState()->IsFullscreen())
       return topmost_window;
     topmost_window = topmost_window->GetTransientParent();
   }
   return nullptr;
 }
 
 }  // namespace wm
 }  // namespace ash