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

src/runtime/runtime-strings.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/regexp/jsregexp-inl.h"
 #include "src/string-builder.h"
 #include "src/string-search.h"
@@ skipping 72 matching lines @@
   }
   if (isolate->has_pending_exception()) return isolate->heap()->exception();
   // In case of empty handle and no pending exception we have stack overflow.
   return isolate->StackOverflow();
 }
 
 
 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());
 }
 
 RUNTIME_FUNCTION(Runtime_SubString) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 3);
 
   CONVERT_ARG_HANDLE_CHECKED(String, string, 0);
   int start, end;
   // We have a fast integer-only case here to avoid a conversion to double in
@@ skipping 872 matching lines @@
 
 RUNTIME_FUNCTION(Runtime_StringCharCodeAt) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 2);
   if (!args[0]->IsString()) return isolate->heap()->undefined_value();
   if (!args[1]->IsNumber()) return isolate->heap()->undefined_value();
   if (std::isinf(args.number_at(1))) return isolate->heap()->nan_value();
   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