[builtins] Move StringLastIndexOf to a builtin.

src/builtins/builtins-string.cc

Index: src/builtins/builtins-string.cc
diff --git a/src/builtins/builtins-string.cc b/src/builtins/builtins-string.cc
index f7413fc30ff6681293e0c8157c4fdc7b5f03e0c8..c09a6b71f77514e33d48af3d82d7acb8882e0dae 100644
--- a/src/builtins/builtins-string.cc
+++ b/src/builtins/builtins-string.cc
@@ -477,6 +477,15 @@ void Builtins::Generate_StringPrototypeCharCodeAt(
   assembler->Return(result);
 }
 
+// ES6 section 21.1.3.9
+// String.prototype.lastIndexOf ( searchString [ , position ] )
+BUILTIN(StringPrototypeLastIndexOf) {
+  HandleScope handle_scope(isolate);
+  return String::LastIndexOf(isolate, args.receiver(),
+                             args.atOrUndefined(isolate, 1),
+                             args.atOrUndefined(isolate, 2));
+}
+
 // ES6 section 21.1.3.10 String.prototype.localeCompare ( that )
 //
 // This function is implementation specific.  For now, we do not