fix #603, support mock objects

test/codegen/language/no_such_method_mock_test.dart

+// Copyright (c) 2011, 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.
+// Dart test program testing that NoSuchMethod is properly called.
+
+import "package:expect/expect.dart";
+
+class Cat {
+  bool eatFood(String food) => true;
+  int scratch(String furniture) => 100;
+}
+
+class MockCat implements Cat {
+  dynamic noSuchMethod(Invocation invocation) {
+    return (invocation.positionalArguments[0] as String).isNotEmpty;
+  }
+}
+
+void main() {
+  MockCat mock = new MockCat();
+  Expect.isTrue((mock as dynamic).eatFood("food"));
+  Expect.isFalse(mock.eatFood(""));
+
+  // In strong mode this will be a runtime type error:
+  // bool is not an int. VM will fail with noSuchMethod +.
+  Expect.throws(() => mock.scratch("couch") + 0);
+}