Beef up the covariant generic parameter tear off test case

pkg/front_end/testcases/runtime_checks/covariant_generic_parameter_tear_off.dart.direct.expect

 library test;
 import self as self;
 import "dart:core" as core;
 
 typedef F<T extends core::Object> = (T) → void;
+typedef G<T extends core::Object, U extends core::Object> = (T) → U;
 class C<T extends core::Object> extends core::Object {
   default constructor •() → void
     : super core::Object::•()
     ;
-  method f(self::C::T x) → void {}
+  method f1(self::C::T x) → void {}
+  method f2(core::List<self::C::T> x) → self::C::T
+    return x.first;
 }
-static method g1(self::C<core::num> c) → void {
-  c.f;
+static method g1(self::C<core::num> c) → (core::num) → void {
+  return c.f1;
 }
 static method g2(self::C<core::int> c, core::Object x) → void {
   (core::Object) → void f = self::g1(c) as (core::Object) → void;
   f.call(x);
 }
+static method g3(self::C<core::num> c) → (core::List<core::num>) → core::num {
+  return c.f2;
+}
 static method test() → void {
   dynamic x = self::g1(new self::C::•<core::int>());
   x.call(1.5);
+  self::g3(new self::C::•<core::int>());
 }
 static method main() → dynamic {}