[builtins] Move StringIndexOf to a builtin.

src/messages.cc

Index: src/messages.cc
diff --git a/src/messages.cc b/src/messages.cc
index cc6349d73c52cfa15b5fb7aa96250ea84ef9b549..b9a8d977fe7611cf69d04fbd949f7828e2201925 100644
--- a/src/messages.cc
+++ b/src/messages.cc
@@ -499,7 +499,11 @@ void AppendFileLocation(Isolate* isolate, JSStackFrame* call_site,
 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