Use a direct include of strings headers in extensions/, google_apis/, gpu/.

extensions/common/error_utils.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.
 
 #ifndef EXTENSIONS_COMMON_ERROR_UTILS_H_
 #define EXTENSIONS_COMMON_ERROR_UTILS_H_
 
 #include <string>
 
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 namespace extensions {
 
 class ErrorUtils {
  public:
   // Creates an error messages from a pattern.
   static std::string FormatErrorMessage(const std::string& format,
                                         const std::string& s1);
 
   static std::string FormatErrorMessage(const std::string& format,
@@ skipping 14 matching lines @@
 
   static string16 FormatErrorMessageUTF16(const std::string& format,
                                           const std::string& s1,
                                           const std::string& s2,
                                           const std::string& s3);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_ERROR_UTILS_H_