fix #29585, implement equality for tearoffs

tests/language_strong/tearoff_dynamic_test.dart

 // Copyright (c) 2016, 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';
 
 class Foo {
   dynamic method(int x) {}
+  dynamic method2(int x) {}
 }
 
 main() {
   Foo foo = new Foo();
 
   dynamic dynamicMethod1 = foo.method;
   Expect.throws(() => dynamicMethod1(2.5));
 
   dynamic dynamicMethod2 = (foo as dynamic).method;
   Expect.throws(() => dynamicMethod2(2.5));
+
+  Expect.equals(dynamicMethod1, dynamicMethod1);
+  Expect.equals(dynamicMethod1, dynamicMethod2);
+  Expect.equals(dynamicMethod1, foo.method);
+  Expect.equals(foo.method2, (foo as dynamic).method2);
+
+  Expect.notEquals(dynamicMethod1, new Foo().method);
+  Expect.notEquals(dynamicMethod1, (new Foo() as dynamic).method);
+  Expect.notEquals(dynamicMethod1, foo.method2);
+  Expect.notEquals(dynamicMethod1, (foo as dynamic).method2);
 }