Add UMA metrics to measure the dismissal cause of dialogs.

chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.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_TAB_HELPER_H_
 #define CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_TAB_HELPER_H_
 
 #include <memory>
 
 #include "base/callback_forward.h"
@@ skipping 46 matching lines @@
                      bool reset_state) override;
 
   // WebContentsObserver:
   void WasHidden() override;
 
   // BrowserListObserver:
   void OnBrowserSetLastActive(Browser* browser) override;
 
  private:
   friend class content::WebContentsUserData<JavaScriptDialogTabHelper>;
+  enum class DismissalCause;
+
+  void LogDialogDismissalCause(DismissalCause cause);
 
   // Wrapper around a DialogClosedCallback so that we can intercept it before
   // passing it onto the original callback.
   void OnDialogClosed(DialogClosedCallback callback,
                       bool success,
                       const base::string16& user_input);
 
   void CloseDialog(bool suppress_callback,
                    bool success,
-                   const base::string16& user_input);
+                   const base::string16& user_input,
+                   DismissalCause cause);
 
   void ClearDialogInfo();
 
   // The dialog being displayed on the observed WebContents.
   base::WeakPtr<JavaScriptDialog> dialog_;
 
+  // The type of dialog being displayed. Only valid when |dialog_| is non-null.
+  content::JavaScriptMessageType message_type_ =
+      content::JavaScriptMessageType::JAVASCRIPT_MESSAGE_TYPE_ALERT;
+
   // The callback provided for when the dialog is closed. Usually the dialog
   // itself calls it, but in the cases where the dialog is closed not by the
   // user's input but by a call to |CloseDialog|, this class will call it.
   content::JavaScriptDialogManager::DialogClosedCallback dialog_callback_;
 
   base::Closure dialog_shown_;
 
   DISALLOW_COPY_AND_ASSIGN(JavaScriptDialogTabHelper);
 };
 
 #endif  // CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_TAB_HELPER_H_