Converts MruWindowTracker to work with common types

ash/common/wm/focus_rules.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_WM_FOCUS_RULES_H_
+#define ASH_COMMON_WM_FOCUS_RULES_H_
+
+#include "ash/ash_export.h"
+
+namespace ash {
+
+class WmWindow;
+
+// These functions provide the ash implementation wm::FocusRules. See
+// description there for details.
+ASH_EXPORT bool IsToplevelWindow(WmWindow* window);
+ASH_EXPORT bool IsWindowConsideredActivatable(WmWindow* window);
+ASH_EXPORT bool IsWindowConsideredVisibleForActivation(WmWindow* window);
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_WM_FOCUS_RULES_H_