net: Append base:: in the StringPrintf calls.

net/http/http_auth_handler.cc

Index: net/http/http_auth_handler.cc
diff --git a/net/http/http_auth_handler.cc b/net/http/http_auth_handler.cc
index 4858658f65d45ee8651f80ae9812b635c8999622..ccb8766b6919938b1c99c35fd03ba014b8cc4453 100644
--- a/net/http/http_auth_handler.cc
+++ b/net/http/http_auth_handler.cc
@@ -7,6 +7,7 @@
 #include "base/histogram.h"
 #include "base/logging.h"
 #include "base/string_util.h"
+#include "base/stringprintf.h"
 #include "net/base/net_errors.h"
 
 namespace net {
@@ -27,7 +28,7 @@ HttpAuthHandler::~HttpAuthHandler() {
 //static
 std::string HttpAuthHandler::GenerateHistogramNameFromScheme(
     const std::string& scheme) {
-  return StringPrintf("Net.AuthGenerateToken_%s", scheme.c_str());
+  return base::StringPrintf("Net.AuthGenerateToken_%s", scheme.c_str());
 }
 
 bool HttpAuthHandler::InitFromChallenge(