Add more string_util functions to base namespace.

net/test/url_request/url_request_slow_download_job.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 "net/test/url_request/url_request_slow_download_job.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/location.h"
 #include "base/logging.h"
@@ skipping 255 matching lines @@
         "Cache-Control: max-age=0\n");
 
     if (base::LowerCaseEqualsASCII(kKnownSizeUrl,
                                    request_->url().spec().c_str())) {
       raw_headers.append(base::StringPrintf(
           "Content-Length: %d\n", kFirstDownloadSize + kSecondDownloadSize));
     }
   }
 
   // ParseRawHeaders expects \0 to end each header line.
-  ReplaceSubstringsAfterOffset(&raw_headers, 0, "\n", std::string("\0", 1));
+  base::ReplaceSubstringsAfterOffset(
+      &raw_headers, 0, "\n", base::StringPiece("\0", 1));
   info->headers = new HttpResponseHeaders(raw_headers);
 }
 
 bool URLRequestSlowDownloadJob::GetMimeType(std::string* mime_type) const {
   HttpResponseInfo info;
   GetResponseInfoConst(&info);
   return info.headers.get() && info.headers->GetMimeType(mime_type);
 }
 
 }  // namespace net