implement `Invocation.typeArguments` in DDC

tests/language_strong/mock_writable_final_field_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';
 
 final values = <int>[];
 
 class Mock {
   noSuchMethod(Invocation i) {
-    Expect.equals(i.memberName.toString(), 'Symbol("_x")');
+    var expected = i.isGetter ? "_x" : "_x=";
+    Expect.equals('Symbol("$expected")', i.memberName.toString());
     values.add(i.positionalArguments[0]);
   }
 }
 
 class Foo {
   int _x;
 }
 
 class Bar extends Mock implements Foo {
   final int _x = 42;
 }
 
 void main() {
   {
     Bar b = new Bar();
     Expect.equals(b._x, 42);
     b._x = 123;
     Expect.listEquals(values, [123]);
     values.clear();
   }
   {
     // It works the same if called statically through the Foo interface.
     Foo b = new Bar();
     Expect.equals(b._x, 42);
     b._x = 123;
     Expect.listEquals(values, [123]);
     values.clear();
   }
 }