anchor.diff:    // Sendables are top-level functions and static functions only.
     testSendable("toplevel", toplevel);
     testSendable("static", C.staticFunc);
  -
     // Unsendables are any closure - instance methods or function expression.
     var c = new C();
     testUnsendable("instance method", c.instanceMethod);
  
positive.code: 
    // Try sending through other isolate.
    asyncStart();
    echoPort((_) => throw "unreachable")
      .then((p) => p.send(func))
      .then((p) => throw "unreachable 2",
            onError: (e, s) {asyncEnd();});
  }
  
negative.code: void _call(initPort) {
    initPort.send(singleMessagePort(callFunc));
  }
  
  void testUnsendable(name, func) {
    asyncStart();
  