base: Get rid of 'using' declaration of StringAppendF.

chrome/service/cloud_print/cloud_print_url_fetcher.cc

Index: chrome/service/cloud_print/cloud_print_url_fetcher.cc
diff --git a/chrome/service/cloud_print/cloud_print_url_fetcher.cc b/chrome/service/cloud_print/cloud_print_url_fetcher.cc
index 3c1e859622b9186bf3118f1578bd5acf36093411..8996a0aab63eaf28d2a7b87cd3c9e88558165ba5 100644
--- a/chrome/service/cloud_print/cloud_print_url_fetcher.cc
+++ b/chrome/service/cloud_print/cloud_print_url_fetcher.cc
@@ -148,7 +148,7 @@ URLRequestContextGetter* CloudPrintURLFetcher::GetRequestContextGetter() {
       new ServiceURLRequestContextGetter();
   // Now set up the user agent for cloudprint.
   std::string user_agent = getter->user_agent();
-  StringAppendF(&user_agent, " %s", kCloudPrintUserAgent);
+  base::StringAppendF(&user_agent, " %s", kCloudPrintUserAgent);
   getter->set_user_agent(user_agent);
   return getter;
 }