mash: Add SystemTrayClient interface, use to show date settings

chrome/browser/ui/ash/system_tray_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 CONTENT_PUBLIC_RENDERER_GUEST_MODE_H_
-#define CONTENT_PUBLIC_RENDERER_GUEST_MODE_H_
+#ifndef CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_COMMON_H_
+#define CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_COMMON_H_
 
 #include "base/macros.h"
-#include "content/common/content_export.h"
 
-namespace content {
-
-class CONTENT_EXPORT GuestMode {
+// System tray code shared between classic ash SystemTrayDelegateChromeos and
+// mustash SystemTrayClient.
+class SystemTrayCommon {
  public:
-  // Returns true if guests could be using cross process frames.
-  static bool UseCrossProcessFramesForGuests();
+  // Shows the settings related to date, timezone etc.
+  static void ShowDateSettings();
 
  private:
-  GuestMode();
-
-  DISALLOW_COPY_AND_ASSIGN(GuestMode);
+  DISALLOW_IMPLICIT_CONSTRUCTORS(SystemTrayCommon);
 };
 
-}  // namespace content
-
-#endif  // CONTENT_PUBLIC_RENDERER_GUEST_MODE_H_
+#endif  // CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_COMMON_H_