Moves MruWindowTracker to WmShell

ash/common/shell_common.h

+// 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_SHELL_COMMON_H_
+#define ASH_COMMON_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 ShellCommon {

[James Cook, 2016/06/08 15:48:21]

I would prefer to call this WmShellCommon and the variables wm_shell_common_,
because it's the common piece of the two WmShell* implementations.

I have had significant confusion in the Shelf code due to variable and class
names, and I'm trying to be very explicit about what is Shelf and what is
WmShelf. I think we should do the same with Shell vs. WmShell.

+ public:
+  ShellCommon();
+  ~ShellCommon();
+
+  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(ShellCommon);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_SHELL_COMMON_H_