Adds WmWindow and converts WindowState to use it

ash/wm/window_state_aura.cc

Index: ash/wm/window_state_aura.cc
diff --git a/ash/wm/window_state_aura.cc b/ash/wm/window_state_aura.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ce3e03f41285b060b0779f5a22cde26a1efde630
--- /dev/null
+++ b/ash/wm/window_state_aura.cc
@@ -0,0 +1,37 @@
+// 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/wm/window_state_aura.h"
+
+#include "ash/wm/aura/wm_window_aura.h"
+#include "ash/wm/window_properties.h"
+#include "ash/wm/window_state.h"
+#include "ash/wm/window_util.h"
+#include "ui/aura/window.h"
+
+namespace ash {
+namespace wm {
+
+WindowState* GetActiveWindowState() {
+  aura::Window* active = GetActiveWindow();
+  return active ? GetWindowState(active) : nullptr;
+}
+
+WindowState* GetWindowState(aura::Window* window) {
+  if (!window)
+    return nullptr;
+  WindowState* settings = window->GetProperty(kWindowStateKey);
+  if (!settings) {
+    settings = new WindowState(WmWindowAura::Get(window));
+    window->SetProperty(kWindowStateKey, settings);
+  }
+  return settings;
+}
+
+const WindowState* GetWindowState(const aura::Window* window) {
+  return GetWindowState(const_cast<aura::Window*>(window));
+}
+
+}  // namespace wm
+}  // namespace ash