Use container::back() and container::pop_back() for content.

content/browser/notifications/notification_id_generator.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 "content/browser/notifications/notification_id_generator.h"
 
 #include <sstream>
 
 #include "base/base64.h"
 #include "base/files/file_path.h"
@@ skipping 87 matching lines @@
 
   stream << kNonPersistentPrefix;
   stream << ComputeBrowserContextHash(browser_context_);
   stream << base::IntToString(browser_context_->IsOffTheRecord());
   stream << origin;
 
   // Non-persistent notification ids are unique per renderer process when no
   // tag is being used. Tags still identify uniqueness for the given origin.
 
   stream << base::IntToString(!tag.empty());
-  if (!tag.size()) {
+  if (tag.empty()) {
     stream << base::IntToString(render_process_id_);
     stream << kSeparator;
 
     stream << base::IntToString(non_persistent_notification_id);
   } else {
     stream << tag;
   }
 
   return stream.str();
 }
 
 }  // namespace content