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

chrome/browser/autocomplete/url_prefix.h

 // 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.
 
 #ifndef CHROME_BROWSER_AUTOCOMPLETE_URL_PREFIX_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_URL_PREFIX_H_
 
 #include <vector>
 
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 struct URLPrefix;
 typedef std::vector<URLPrefix> URLPrefixes;
 
 // A URL prefix; combinations of schemes and (least significant) domain labels
 // that may be inferred from certain URL-like input strings.
 struct URLPrefix {
   URLPrefix(const string16& prefix, size_t num_components);
 
   // Returns a vector of URL prefixes sorted by descending number of components.
@@ skipping 11 matching lines @@
 
   string16 prefix;
 
   // The number of URL components (scheme, domain label, etc.) in the prefix.
   // For example, "http://foo.com" and "www.bar.com" each have one component,
   // while "ftp://ftp.ftp.com" has two, and "mysite.com" has none.
   size_t num_components;
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_URL_PREFIX_H_