mash: Migrate ScopedTargetRootWindow to //ash/common

ash/aura/scoped_root_window_for_new_windows_aura.cc

Index: ash/aura/scoped_root_window_for_new_windows_aura.cc
diff --git a/ash/scoped_target_root_window.cc b/ash/aura/scoped_root_window_for_new_windows_aura.cc
similarity index 49%
rename from ash/scoped_target_root_window.cc
rename to ash/aura/scoped_root_window_for_new_windows_aura.cc
index 9213b3ad54cf56fe3f0cee0757073445ffc5604c..37e4b927918ad50e7083d12d697028a5272d34a9 100644
--- a/ash/scoped_target_root_window.cc
+++ b/ash/aura/scoped_root_window_for_new_windows_aura.cc
@@ -1,18 +1,20 @@
 // 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/scoped_target_root_window.h"
+
+#include "ash/aura/scoped_root_window_for_new_windows_aura.h"
 
 #include "ash/shell.h"
 
 namespace ash {
 
-ScopedTargetRootWindow::ScopedTargetRootWindow(aura::Window* root_window) {
+ScopedRootWindowForNewWindowsAura::ScopedRootWindowForNewWindowsAura(
+    aura::Window* root_window) {
   Shell::GetInstance()->scoped_target_root_window_ = root_window;

[msw, 2016/08/01 21:36:14]

q: [D]CHECK that scoped_target_root_window_ is null?

 }
 
-ScopedTargetRootWindow::~ScopedTargetRootWindow() {
-  Shell::GetInstance()->scoped_target_root_window_ = NULL;
+ScopedRootWindowForNewWindowsAura::~ScopedRootWindowForNewWindowsAura() {
+  Shell::GetInstance()->scoped_target_root_window_ = nullptr;

[msw, 2016/08/01 21:36:15]

q: [D]CHECK that the existing value was set by this instance?

 }
 
 }  // namespace ash