Use int32_t for duration property of toast

ash/system/toast/toast_data.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_SYSTEM_TOAST_TOAST_DATA_H_
 #define ASH_SYSTEM_TOAST_TOAST_DATA_H_
 
 #include <string>
 
 #include "ash/ash_export.h"
 
 namespace ash {
 
 struct ASH_EXPORT ToastData {
-  ToastData(const std::string& id,
-            const std::string& text,
-            uint64_t duration_ms)
+  ToastData(const std::string& id, const std::string& text, int32_t duration_ms)
       : id(id), text(text), duration_ms(duration_ms) {}
 
   std::string id;
   std::string text;
-  uint64_t duration_ms;
+  int32_t duration_ms;
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TOAST_TOAST_DATA_H_