[ios] Add new ntp histogram type.

ios/chrome/browser/metrics/new_tab_page_uma.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 IOS_CHROME_BROWSER_METRICS_NEW_TAB_PAGE_UMA_H_
 #define IOS_CHROME_BROWSER_METRICS_NEW_TAB_PAGE_UMA_H_
 
 #include "ui/base/page_transition_types.h"
 
 namespace ios {
 class ChromeBrowserState;
 }  // namespace ios
 
 class GURL;
 
 // This namespace provides various helpers around handling NTP Uma calls.
 namespace new_tab_page_uma {
 
 enum ActionType {
   ACTION_SEARCHED_USING_OMNIBOX,
   ACTION_NAVIGATED_TO_GOOGLE_HOMEPAGE,
   ACTION_NAVIGATED_USING_OMNIBOX,
   ACTION_OPENED_MOST_VISITED_ENTRY,
   ACTION_OPENED_RECENTLY_CLOSED_ENTRY,
   ACTION_OPENED_BOOKMARK,
   ACTION_OPENED_FOREIGN_SESSION,
+  ACTION_OPENED_DOODLE,
   NUM_ACTION_TYPES,
 };
 
 void RecordAction(ios::ChromeBrowserState* browserState, ActionType action);
 void RecordActionFromOmnibox(ios::ChromeBrowserState* browserState,
                              const GURL& url,
                              ui::PageTransition transition);
 }  // namespace new_tab_page_uma
 
 #endif  // IOS_CHROME_BROWSER_METRICS_NEW_TAB_PAGE_UMA_H_