[builtins] Move StringIndexOf to a builtin.

src/messages.cc

 // Copyright 2011 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/messages.h"
 
 #include <memory>
 
 #include "src/api.h"
 #include "src/execution.h"
@@ skipping 481 matching lines @@
       Handle<String> column_string = isolate->factory()->NumberToString(
           handle(Smi::FromInt(column_number), isolate), isolate);
       builder->AppendString(column_string);
     }
   }
 }
 
 int StringIndexOf(Isolate* isolate, Handle<String> subject,
                   Handle<String> pattern) {
   if (pattern->length() > subject->length()) return -1;
-  return String::IndexOf(isolate, subject, pattern, 0);
+  Object* index = String::IndexOf(isolate, subject, pattern,
+                                  isolate->factory()->undefined_value());
+  int index_int;
+  if (index->ToInt32(&index_int)) return index_int;
+  return -1;
 }
 
 // Returns true iff
 // 1. the subject ends with '.' + pattern, or
 // 2. subject == pattern.
 bool StringEndsWithMethodName(Isolate* isolate, Handle<String> subject,
                               Handle<String> pattern) {
   if (String::Equals(subject, pattern)) return true;
 
   FlatStringReader subject_reader(isolate, String::Flatten(subject));
@@ skipping 586 matching lines @@
   DCHECK(mode != SKIP_UNTIL_SEEN);
 
   Handle<Object> no_caller;
   Handle<String> msg = FormatMessage(isolate, template_index, arg0, arg1, arg2);
   return ErrorUtils::Construct(isolate, constructor, constructor, msg, mode,
                                no_caller, false);
 }
 
 }  // namespace internal
 }  // namespace v8