Use a direct include of strings headers in chrome/browser/d*/.

chrome/browser/download/download_extensions.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 <set>
 #include <string>
 
 #include "chrome/browser/download/download_extensions.h"
 
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "net/base/mime_util.h"
 #include "net/base/net_util.h"
 
 namespace download_util {
 
 // For file extensions taken from mozilla:
 
 /* ***** BEGIN LICENSE BLOCK *****
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  *
@@ skipping 250 matching lines @@
   for (size_t i = 0; i < arraysize(kExecutableBlackList); ++i) {
     if (net::MatchesMimeType(kExecutableBlackList[i], mime_type))
       return false;
   }
   // We consider only other application types to be executable.
   return net::MatchesMimeType("application/*", mime_type);
 }
 
 
 }  // namespace download_util