Begin writing tests of the runtime checks needed for Dart 2.0 soundness.

pkg/front_end/testcases/runtime_checks/contravariant_generic_return_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> = () → (T) → void;
+class C<T extends core::Object> extends core::Object {
+  field (self::C::T) → void _x;
+  constructor •((self::C::T) → void _x) → void
+    : self::C::_x = _x, super core::Object::•()
+    ;
+  method f() → (self::C::T) → void
+    return this._x;
+}
+static method g(self::C<core::num> c) → () → (core::num) → void {
+  return c.f;
+}
+static method h(core::int i) → void {
+  core::print("${i}");
+}
+static method test() → void {
+  dynamic x = self::g(new self::C::•<core::int>(self::h));
+}
+static method main() → void {}