Use a direct include of strings headers in chrome/installer/, part 2.

chrome/installer/util/user_experiment.h

 // Copyright 2013 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.
 //
 // This files declares a class that contains methods and data to conduct
 // for user expeirments.
 
 #ifndef CHROME_INSTALLER_UTIL_USER_EXPERIMENT_H_
 #define CHROME_INSTALLER_UTIL_USER_EXPERIMENT_H_
 
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "chrome/installer/util/util_constants.h"
 
 class CommandLine;
 
 namespace base {
 class FilePath;
 }
 
 namespace installer {
 
@@ skipping 37 matching lines @@
 // The user has qualified for the inactive user toast experiment and this
 // function just performs it.
 void InactiveUserToastExperiment(int flavor,
                                  const string16& experiment_group,
                                  const Product& product,
                                  const base::FilePath& application_path);
 
 }  // namespace installer
 
 #endif  // CHROME_INSTALLER_UTIL_USER_EXPERIMENT_H_