Add more string_util functions to base namespace.

ash/system/user/login_status.cc

Index: ash/system/user/login_status.cc
diff --git a/ash/system/user/login_status.cc b/ash/system/user/login_status.cc
index 0e218654af35c1c2f55073d42291124045a89170..fa5103af73341f68beea09a22c10cf74c6cfa773 100644
--- a/ash/system/user/login_status.cc
+++ b/ash/system/user/login_status.cc
@@ -41,7 +41,8 @@ base::string16 GetLocalizedSignOutStringForStatus(LoginStatus status,
   // spaces are substituted.
   base::string16 newline = multiline ? base::ASCIIToUTF16("\n")
                                      : base::ASCIIToUTF16(" ");
-  ReplaceSubstringsAfterOffset(&message, 0, base::ASCIIToUTF16("\\n"), newline);
+  base::ReplaceSubstringsAfterOffset(
+      &message, 0, base::ASCIIToUTF16("\\n"), newline);
   return message;
 }