Migrate test block 47 and downstream dependencies to Dart 2.0.

tests/language_2/checked_setter3_test.dart

+// Copyright (c) 2013, 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 A<T> {
+  T field;
+}
+
+class B<T> {
+  T field = 42; //# 01: compile-time error
+}
+
+class C<T> {
+  T field = 42; //# 02: compile-time error
+}
+
+main() {
+  var a = new A<String>();
+  var c = new C<int>();
+  var i = 42;
+  var s = 'foo';
+  Expect.throws(() => a.field = i, (e) => e is TypeError); //# 03: compile-time error

[bkonyi, 2017/08/09 16:23:03]

Same as the last comment. I'm pretty sure we can do away with Expect.throws(...)
for these sort of changes, right?

[jcollins, 2017/08/15 14:55:15]

Done.

+}