Add UserAction when the user opens ReadingList

ios/chrome/browser/ui/tools_menu/tools_popup_controller.mm

 // Copyright 2012 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.
 
 #import "ios/chrome/browser/ui/tools_menu/tools_popup_controller.h"
 
 #import <QuartzCore/QuartzCore.h>
 
 #include "base/logging.h"
 #include "base/mac/scoped_nsobject.h"
@@ skipping 204 matching lines @@
       self.containerView.hidden = YES;
       base::RecordAction(UserMetricsAction("MobileMenuReportAnIssue"));
       break;
     case IDC_VIEW_SOURCE:
       // Debug only; no metric.
       break;
     case IDC_SHOW_TOOLS_MENU:
       // Do nothing when tapping the tools menu a second time.
       break;
     case IDC_SHOW_READING_LIST:
-      // TODO(crbug.com/582957): Add metric here.
+      base::RecordAction(UserMetricsAction("MobileMenuReadingList"));
       break;
     default:
       NOTREACHED();
       break;
   }
 
   // Close the menu.
   [self.delegate dismissPopupMenu:self];
 }
 
 @end