fix #30423, covariant parameter tearoff type should be Object

tests/language_strong/covariant_subtyping_test.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 import 'package:expect/expect.dart';
 
 bool isTypeError(e) => e is TypeError;
 
 class Fields<T> {
   T x;
   T _y;
@@ skipping 203 matching lines @@
 testCallMethod() {
   ClassF<int> cc = new ClassF<int>();
   ClassF<Object> ca = cc; // An upcast, per covariance.
   F<Object> f = ca;
   Expect.equals(f.runtimeType.toString(), 'ClassF<int>');
   Expect.throws(() {
     f(new Object());
   }, isTypeError);
 }
 
+class TearOff<T> {
+  method1(T t) => null; // needs check
+  method2(Function(T) takesT) => null;
+  method3(T Function() returnsT) => null; // needs check
+  method4(Function(Function(T)) takesTakesT) => null; // needs check
+  method5(Function(T Function()) takesReturnsT) => null;
+  method6(Function(T) Function() returnsTakesT) => null;
+  method7(T Function() Function() returnsReturnsT) => null; // needs check
+}
+
+testTearOffRuntimeType() {
+  expectRTTI(tearoff, type) => Expect.equals('${tearoff.runtimeType}', type,
+      'covariant params should reify with Object as their type');
+
+  TearOff<num> t = new TearOff<int>();
+  expectRTTI(t.method1, '(Object) -> dynamic');
+
+  expectRTTI(t.method2, '((int) -> dynamic) -> dynamic');
+  expectRTTI(t.method3, '(Object) -> dynamic');
+
+  expectRTTI(t.method4, '(Object) -> dynamic');
+  expectRTTI(t.method5, '((() -> int) -> dynamic) -> dynamic');
+  expectRTTI(t.method6, '(() -> (int) -> dynamic) -> dynamic');
+  expectRTTI(t.method7, '(Object) -> dynamic');
+}
+
 main() {
   testField();
   testPrivateFields();
   testClassBounds();
   testReturnOfFunctionType();
   testTearoffReturningFunctionType();
   testFieldOfFunctionType();
   testFieldOfGenericFunctionType();
   testMixinApplication();
   testGenericMethodBounds();
   testCallMethod();
+  testTearOffRuntimeType();
 }