Moves MruWindowTracker to WmShell

ash/common/wm_shell_common.h

Index: ash/common/wm_shell_common.h
diff --git a/ash/common/wm_shell_common.h b/ash/common/wm_shell_common.h
new file mode 100644
index 0000000000000000000000000000000000000000..e84d4162cdfc7c75029eb5f0b49b280860f4e268
--- /dev/null
+++ b/ash/common/wm_shell_common.h
@@ -0,0 +1,36 @@
+// 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.
+
+#ifndef ASH_COMMON_WM_SHELL_COMMON_H_
+#define ASH_COMMON_WM_SHELL_COMMON_H_
+
+#include <memory>
+
+#include "ash/ash_export.h"
+#include "base/macros.h"
+
+namespace ash {
+
+class MruWindowTracker;
+
+// Contains code used by both shell implementations.
+class ASH_EXPORT WmShellCommon {
+ public:
+  WmShellCommon();
+  ~WmShellCommon();
+
+  MruWindowTracker* mru_window_tracker() { return mru_window_tracker_.get(); }
+
+  void CreateMruWindowTracker();
+  void DeleteMruWindowTracker();
+
+ private:
+  std::unique_ptr<MruWindowTracker> mru_window_tracker_;
+
+  DISALLOW_COPY_AND_ASSIGN(WmShellCommon);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_WM_SHELL_COMMON_H_