Adds views::corewm::WMState to install common state

ui/views/corewm/wm_state.cc

Index: ui/views/corewm/wm_state.cc
diff --git a/ui/views/corewm/wm_state.cc b/ui/views/corewm/wm_state.cc
new file mode 100644
index 0000000000000000000000000000000000000000..07992479d64cfa8521b269a29dc04332d6aaa250
--- /dev/null
+++ b/ui/views/corewm/wm_state.cc
@@ -0,0 +1,23 @@
+// Copyright (c) 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 "ui/views/corewm/wm_state.h"
+
+#include "ui/views/corewm/transient_window_stacking_client.h"
+
+namespace views {
+namespace corewm {
+
+WMState::WMState()
+    : window_stacking_client_(new TransientWindowStackingClient) {
+  aura::client::SetWindowStackingClient(window_stacking_client_.get());
+}
+
+WMState::~WMState() {
+  if (aura::client::GetWindowStackingClient() == window_stacking_client_.get())
+    aura::client::SetWindowStackingClient(NULL);
+}
+
+}  // namespace corewm
+}  // namespace views