Hide dismiss button on toast when doing partial screenshot using stylus tools.

ash/common/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_COMMON_SYSTEM_TOAST_TOAST_DATA_H_
 #define ASH_COMMON_SYSTEM_TOAST_TOAST_DATA_H_
 
 #include <string>
 
 #include "ash/ash_export.h"
+#include "base/optional.h"
 #include "base/strings/string16.h"
 
 namespace ash {
 
 struct ASH_EXPORT ToastData {
   // "|duration_ms| == -1" means the toast view should be displayed until the
   // dismiss button is clicked.
   static const int32_t kInfiniteDuration = -1;
 
   ToastData(std::string id,
             const base::string16& text,
             int32_t duration_ms,
-            const base::string16& dismiss_text);
+            const base::Optional<base::string16>& dismiss_text);
   ToastData(const ToastData& other);
+  ~ToastData();
 
   std::string id;
   base::string16 text;
   int32_t duration_ms;
-  base::string16 dismiss_text;
+  base::Optional<base::string16> dismiss_text;
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TOAST_TOAST_DATA_H_