MD History: Add tooltip for history menu button

chrome/browser/ui/webui/md_history_ui.cc

 // Copyright 2015 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.
 
 #include "chrome/browser/ui/webui/md_history_ui.h"
 
 #include "base/command_line.h"
 #include "build/build_config.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/signin/signin_manager_factory.h"
@@ skipping 39 matching lines @@
                              IDS_HISTORY_DELETE_PRIOR_VISITS_CONFIRM_BUTTON);
   source->AddLocalizedString("deleteSession",
                              IDS_HISTORY_OTHER_SESSIONS_HIDE_FOR_NOW);
   source->AddLocalizedString(
       "deleteWarning", IDS_HISTORY_DELETE_PRIOR_VISITS_WARNING_NO_INCOGNITO);
   source->AddLocalizedString("expandSessionButton",
                              IDS_HISTORY_OTHER_SESSIONS_EXPAND_SESSION);
   source->AddLocalizedString("foundSearchResults",
                              IDS_HISTORY_FOUND_SEARCH_RESULTS);
   source->AddLocalizedString("historyInterval", IDS_HISTORY_INTERVAL);
+  source->AddLocalizedString("historyMenuButton",
+                             IDS_MD_HISTORY_HISTORY_MENU_DESCRIPTION);
   source->AddLocalizedString("historyMenuItem",
                              IDS_MD_HISTORY_HISTORY_MENU_ITEM);
   source->AddLocalizedString("itemsSelected", IDS_MD_HISTORY_ITEMS_SELECTED);
   source->AddLocalizedString("loading", IDS_HISTORY_LOADING);
   source->AddLocalizedString("moreActionsButton",
                              IDS_HISTORY_ACTION_MENU_DESCRIPTION);
   source->AddLocalizedString("moreFromSite", IDS_HISTORY_MORE_FROM_SITE);
   source->AddLocalizedString("openAll", IDS_HISTORY_OTHER_SESSIONS_OPEN_ALL);
   source->AddLocalizedString("openTabsMenuItem",
                              IDS_MD_HISTORY_OPEN_TABS_MENU_ITEM);
@@ skipping 146 matching lines @@
   base::FeatureList::ClearInstanceForTesting();
   base::FeatureList::SetInstance(std::move(feature_list));
 }
 
 // static
 base::RefCountedMemory* MdHistoryUI::GetFaviconResourceBytes(
     ui::ScaleFactor scale_factor) {
   return ResourceBundle::GetSharedInstance().LoadDataResourceBytesForScale(
       IDR_HISTORY_FAVICON, scale_factor);
 }