Add more string_util functions to base namespace.

content/test/net/url_request_abort_on_end_job.cc

Index: content/test/net/url_request_abort_on_end_job.cc
diff --git a/content/test/net/url_request_abort_on_end_job.cc b/content/test/net/url_request_abort_on_end_job.cc
index 3fd494f21152424de35ba1c8d66a79580e21e24e..f7ff5a9dd84bf0f1e759e62211fddbbb74fb0035 100644
--- a/content/test/net/url_request_abort_on_end_job.cc
+++ b/content/test/net/url_request_abort_on_end_job.cc
@@ -76,7 +76,8 @@ void URLRequestAbortOnEndJob::GetResponseInfoConst(
     NOTREACHED();
   }
   // 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 net::HttpResponseHeaders(raw_headers);
 }