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

src/runtime/runtime-strings.cc

Index: src/runtime/runtime-strings.cc
diff --git a/src/runtime/runtime-strings.cc b/src/runtime/runtime-strings.cc
index 328bdceb376c469e90c103c9464732415ba527e4..e6f21e1341af450a2f140332173698185341d05e 100644
--- a/src/runtime/runtime-strings.cc
+++ b/src/runtime/runtime-strings.cc
@@ -90,13 +90,12 @@ RUNTIME_FUNCTION(Runtime_StringReplaceOneCharWithString) {
 RUNTIME_FUNCTION(Runtime_StringIndexOf) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 3);
-  return String::IndexOf(isolate, args.at<Object>(0), args.at<Object>(1),
-                         args.at<Object>(2));
+  return String::IndexOf(isolate, args.at(0), args.at(1), args.at(2));
 }
 
 RUNTIME_FUNCTION(Runtime_StringLastIndexOf) {
   HandleScope handle_scope(isolate);
-  return String::LastIndexOf(isolate, args.at<Object>(0), args.at<Object>(1),
+  return String::LastIndexOf(isolate, args.at(0), args.at(1),
                              isolate->factory()->undefined_value());
 }
 
@@ -989,5 +988,13 @@ RUNTIME_FUNCTION(Runtime_StringCharCodeAt) {
   return __RT_impl_Runtime_StringCharCodeAtRT(args, isolate);
 }
 
+// ES6 #sec-string.prototype.indexof
+// String.prototype.indexOf(searchString [, position])
+RUNTIME_FUNCTION(Runtime_StringPrototypeIndexOf) {
+  HandleScope handle_scope(isolate);
+  DCHECK(args.length() == 3);
+  return String::IndexOf(isolate, args.at(0), args.at(1), args.at(2));
+}
+
 }  // namespace internal
 }  // namespace v8