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

chrome/installer/util/installer_util_test_common.cc

 // Copyright (c) 2011 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/installer/util/installer_util_test_common.h"
 
 #include <windows.h>
 #include <shellapi.h>
 
 #include "base/files/file_path.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 namespace installer {
 
 namespace test {
 
 bool CopyFileHierarchy(const base::FilePath& from, const base::FilePath& to) {
   // In SHFILEOPSTRUCT below, |pFrom| and |pTo| have to be double-null
   // terminated: http://msdn.microsoft.com/library/bb759795.aspx
   string16 double_null_from(from.value());
   double_null_from.push_back(L'\0');
   string16 double_null_to(to.value());
   double_null_to.push_back(L'\0');
 
   SHFILEOPSTRUCT file_op = {};
   file_op.wFunc = FO_COPY;
   file_op.pFrom = double_null_from.c_str();
   file_op.pTo = double_null_to.c_str();
   file_op.fFlags = FOF_NO_UI;
 
   return (SHFileOperation(&file_op) == 0 && !file_op.fAnyOperationsAborted);
 }
 
 }  // namespace test
 
 }  // namespace installer