ChromeOS: Per-user time zone: refactor tests first.

chrome/browser/chromeos/scoped_sys_info_chromeos_version_for_testing.h

+// Copyright 2017 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 SCOPED_SYS_INFO_CHROMEOS_VERSION_FOR_TESTING_H_
+#define SCOPED_SYS_INFO_CHROMEOS_VERSION_FOR_TESTING_H_
+
+#include <string>
+
+#include "base/time/time.h"
+
+namespace chromeos {
+
+// unit_tests must always reset status of modified global singletons,
+// otherwise later tests will fail, because they are run in the same process.
+class ScopedSetRunningOnChromeOSForTesting {
+ public:
+  ScopedSetRunningOnChromeOSForTesting(const std::string& lsb_release,
+                                       const base::Time& lsb_release_time);
+  ~ScopedSetRunningOnChromeOSForTesting();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ScopedSetRunningOnChromeOSForTesting);
+};
+
+}  // namespace chromeos
+
+#endif  //  SCOPED_SYS_INFO_CHROMEOS_VERSION_FOR_TESTING_H_