Reland "Merge more Kernel infrastructure from kernel_sdk SDK fork."

tests/kernel/unsorted/as_is_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.
+
+// Tests of class literals, is, and as expressions.
+
+import 'expect.dart';
+
+class C {}
+
+class D extends C {}
+
+test0() => C;
+test1() => D;
+
+main() {
+  var c = new C();
+  var d = new D();
+  Expect.isTrue(test0() == C);
+  Expect.isTrue(test1() == D);
+  Expect.isTrue(c is C);
+  Expect.isTrue(c is! D);
+  Expect.isTrue(d is C);
+  Expect.isTrue(d is D);
+  Expect.isTrue(c as C == c);
+  Expect.isTrue(d as C == d);
+  Expect.isTrue(d as D == d);
+}