[runtime] Port simple String.prototype.indexOf cases to TF Builtin

src/arguments.h

Index: src/arguments.h
diff --git a/src/arguments.h b/src/arguments.h
index d5d2c02bf068d87a4851090fc2b8a27b09a5fc1e..965232438a9b9be87984a5a46903d865b5b969ff 100644
--- a/src/arguments.h
+++ b/src/arguments.h
@@ -41,7 +41,8 @@ class Arguments BASE_EMBEDDED {
                                         index * kPointerSize));
   }
 
-  template <class S> Handle<S> at(int index) {
+  template <class S = Object>
+  Handle<S> at(int index) {
     Object** value = &((*this)[index]);
     // This cast checks that the object we're accessing does indeed have the
     // expected type.