Moves couple of WmShell methods to standalone functions

ash/common/wm/mru_window_tracker.cc

 // Copyright 2013 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/mru_window_tracker.h"
 
 #include <algorithm>
 
 #include "ash/common/wm/focus_rules.h"
 #include "ash/common/wm/switchable_windows.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
 #include "ash/public/cpp/shell_window_ids.h"
 #include "ash/shell.h"
+#include "ash/wm/window_util.h"
 #include "base/bind.h"
 #include "ui/aura/window.h"
 #include "ui/wm/public/activation_client.h"
 
 namespace ash {
 
 namespace {
 
 using CanActivateWindowPredicate = base::Callback<bool(WmWindow*)>;
 
@@ skipping 93 matching lines @@
   return BuildWindowListInternal(nullptr,
                                  base::Bind(&IsWindowConsideredActivatable));
 }
 
 void MruWindowTracker::SetIgnoreActivations(bool ignore) {
   ignore_window_activations_ = ignore;
 
   // If no longer ignoring window activations, move currently active window
   // to front.
   if (!ignore)
-    SetActiveWindow(WmShell::Get()->GetActiveWindow());
+    SetActiveWindow(WmWindow::Get(wm::GetActiveWindow()));
 }
 
 //////////////////////////////////////////////////////////////////////////////
 // MruWindowTracker, private:
 
 void MruWindowTracker::SetActiveWindow(WmWindow* active_window) {
   if (!active_window)
     return;
 
   std::list<WmWindow*>::iterator iter =
@@ skipping 15 matching lines @@
 
 void MruWindowTracker::OnWindowDestroyed(aura::Window* window) {
   // It's possible for OnWindowActivated() to be called after
   // OnWindowDestroying(). This means we need to override OnWindowDestroyed()
   // else we may end up with a deleted window in |mru_windows_|.
   mru_windows_.remove(WmWindow::Get(window));
   window->RemoveObserver(this);
 }
 
 }  // namespace ash