Add more string_util functions to base namespace.

mojo/runner/context.cc

Index: mojo/runner/context.cc
diff --git a/mojo/runner/context.cc b/mojo/runner/context.cc
index 6eed031ad252c30c266f7474c21dec90add43bc7..e23c2b720ea8914b7bfc58c3003516cde687a63c 100644
--- a/mojo/runner/context.cc
+++ b/mojo/runner/context.cc
@@ -131,7 +131,7 @@ void InitContentHandlers(shell::ApplicationManager* manager,
   //     (to embed a comma into a string escape it using "\,")
   // Whatever takes 'parameters' and constructs a CommandLine is failing to
   // un-escape the commas, we need to move this fix to that file.
-  ReplaceSubstringsAfterOffset(&handlers_spec, 0, "\\,", ",");
+  base::ReplaceSubstringsAfterOffset(&handlers_spec, 0, "\\,", ",");
 #endif
 
   std::vector<std::string> parts;