Use internal const-constructor.

BUG= http://dartbug.com/25760
R=lrn@google.com

Review URL: https://codereview.chromium.org/1696453002 .

CHANGELOG.md

@@ -17,6 +17,8 @@
     The method now only supports one argument for the PEM file name containing
     the trusted certificates.
   * Added support to SecurityContext for PKCS12 certificate and key containers.
+* `dart:async`
+  * Made `StreamView` class a `const` class.
 
 ## 1.14.2 - 2016-02-09
 

sdk/lib/async/stream.dart

@@ -1495,7 +1495,7 @@ abstract class EventSink<T> implements Sink<T> {
 class StreamView<T> extends Stream<T> {
   final Stream<T> _stream;
 
-  StreamView(this._stream);
+  const StreamView(Stream<T> stream) : _stream = stream, super._internal();
 
   bool get isBroadcast => _stream.isBroadcast;
 

tests/lib/async/stream_view_test.dart

@@ -0,0 +1,37 @@
+// 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);