Add a Cocoa version of the auto-dismissing dialog.

chrome/browser/ui/javascript_dialogs/javascript_dialog.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 CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_H_
+#define CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_H_
+
+class JavaScriptDialog {
+ public:
+  virtual ~JavaScriptDialog();
+
+  // Closes the dialog without sending a callback. This is useful when the
+  // JavaScriptDialogTabHelper needs to make this dialog go away so that it can
+  // respond to a call that requires it to make no callback or make a customized
+  // one.
+  virtual void CloseDialogWithoutCallback() = 0;
+};
+
+#endif  // CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_H_