Hide source for builtin functions in toString() call....

src/runtime.cc

Index: src/runtime.cc
===================================================================
--- src/runtime.cc	(revision 2905)
+++ src/runtime.cc	(working copy)
@@ -1208,7 +1208,15 @@
                                                       : Heap::false_value();
 }
 
+static Object* Runtime_FunctionIsBuiltin(Arguments args) {
+  NoHandleAllocation ha;
+  ASSERT(args.length() == 1);
 
+  CONVERT_CHECKED(JSFunction, f, args[0]);
+  return f->IsBuiltin() ? Heap::true_value() : Heap::false_value();
+}
+
+
 static Object* Runtime_SetCode(Arguments args) {
   HandleScope scope;
   ASSERT(args.length() == 2);