Replace string16 with base::string16.

chrome/browser/background/background_mode_manager_gtk.cc

 // Copyright (c) 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.
 
 #include <unistd.h>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/environment.h"
 #include "base/files/file_path.h"
@@ skipping 59 matching lines @@
                             base::Bind(DisableLaunchOnStartupCallback));
   }
 }
 
 void BackgroundModeManager::DisplayAppInstalledNotification(
     const Extension* extension) {
   // TODO(atwilson): Display a platform-appropriate notification here.
   // http://crbug.com/74970
 }
 
-string16 BackgroundModeManager::GetPreferencesMenuLabel() {
-  string16 result = gtk_util::GetStockPreferencesMenuLabel();
+base::string16 BackgroundModeManager::GetPreferencesMenuLabel() {
+  base::string16 result = gtk_util::GetStockPreferencesMenuLabel();
   if (!result.empty())
     return result;
   return l10n_util::GetStringUTF16(IDS_PREFERENCES);
 }