Fix broken vs2012 build

base/stl_util.h

 // 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.
 
 // Derived from google3/util/gtl/stl_util.h
 
 #ifndef BASE_STL_UTIL_H_
 #define BASE_STL_UTIL_H_
 
 #include <algorithm>
+#include <functional>
 #include <string>
 #include <vector>
 
 #include "base/logging.h"
 
 // Clears internal memory of an STL object.
 // STL clear()/reserve(0) does not always free internal memory allocated
 // This function uses swap/destructor to ensure the internal memory is freed.
 template<class T>
 void STLClearObject(T* obj) {
@@ skipping 191 matching lines @@
   ResultType difference;
   std::set_difference(a1.begin(), a1.end(),
                       a2.begin(), a2.end(),
                       std::inserter(difference, difference.end()));
   return difference;
 }
 
 }  // namespace base
 
 #endif  // BASE_STL_UTIL_H_