mash: Move system tray cast code into //ash/common

ash/test/tray_cast_test_api.h

 // Copyright 2015 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_TEST_TRAY_CAST_TEST_API_H_
 #define ASH_TEST_TRAY_CAST_TEST_API_H_
 
 #include <string>
 
 #include "ash/ash_export.h"
-#include "ash/system/cast/tray_cast.h"
+#include "ash/common/system/cast/tray_cast.h"
 #include "base/macros.h"
 
 namespace ash {
 
 class TrayCastTestAPI {
  public:
   explicit TrayCastTestAPI(TrayCast* tray_cast);
   ~TrayCastTestAPI();
 
   bool IsTrayInitialized() const;
@@ skipping 28 matching lines @@
 
   // Not owned.
   TrayCast* tray_cast_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayCastTestAPI);
 };
 
 }  // namespace ash
 
 #endif  // ASH_TEST_TRAY_CAST_TEST_API_H_