Use internal const-constructor.

tests/lib/async/stream_view_test.dart

+// Copyright (c) 2015, 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 the StreamView class.
+
+import "package:expect/expect.dart";
+import "dart:async";
+import "package:async_helper/async_helper.dart";
+
+main() {
+  asyncStart();
+  runTest().whenComplete(asyncEnd);
+}
+
+Future runTest() async {
+  unreachable([a,b]) { throw "UNREACHABLE"; }
+  int tick = 0;
+  ticker() { tick++; }
+
+  asyncStart();
+
+  // Is const constructor.
+  Stream<int> s = const StreamView<int>(const Stream<int>.empty());
+
+  Expect.isFalse(s is Stream<String>);  // Respects type parameter.
+  StreamSubscription<int> sub =
+     s.listen(unreachable, onError: unreachable, onDone: ticker);
+  Expect.isFalse(sub is StreamSubscription<String>);  // Type parameter in sub.
+
+  Stream iterableStream = new Stream.fromIterable([1, 2, 3]);
+  Expect.listEquals([1, 2, 3], await iterableStream.toList());
+
+  asyncEnd();
+}
+
+Future flushMicrotasks() => new Future.delayed(Duration.ZERO);