Dart2js calls method on undefined in checked mode.

[lrhn]

The following code generates a call to .toString$0() on an undefined value.

Object foo() => null;
class D{}
main() {
  var on = foo();
  D od = on;
  od.toString();
}

[peter-ahe-google]

The program fails in checked mode.

This slightly simpler version also fails:

Object foo() => null;
class D{}
main() {
  D od = foo();
  od.toString();
}

---

cc @floitschG.
Added this to the M1 milestone.

[floitschG]

Set owner to @floitschG.
Removed Priority-Medium label.
Added Priority-High, Accepted labels.

[floitschG]

Changed the title to: "Dart2js calls method on undefined in checked mode.".

[floitschG]

Fixed in r9062.

---

Added Fixed label.