Let the stream of File:openRead handle cancel correctly.

tests/standalone/io/file_stream_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 "dart:async";
+import "dart:io";
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+
+void testPauseResumeCancelStream() {
+  asyncStart();
+  Directory.systemTemp.createTemp('file_stream').then((d) {
+    var file = new File("${d.path}/file");
+    new File(Platform.executable).openRead().pipe(file.openWrite())
+      .then((_) {
+        var subscription;
+        subscription = file.openRead().listen((data) {
+          subscription.pause();
+          subscription.resume();
+          void close() {
+            d.deleteSync(recursive: true);
+            asyncEnd();
+          }
+          var future = subscription.cancel();
+          if (future != null) {
+            future.whenComplete(close);
+          } else {
+            close();
+          }
+        }, onDone: () {
+          Expect.fail('the stream was canceled, onDone should not happend');
+        });
+      });
+  });
+}
+
+void testStreamIsEmpty() {
+  asyncStart();
+  Directory.systemTemp.createTemp('file_stream').then((d) {
+    var file = new File("${d.path}/file");
+    new File(Platform.executable).openRead().pipe(file.openWrite())
+      .then((_) {
+        // isEmpty will cancel the stream after first data event.
+        file.openRead().isEmpty.then((empty) {
+          Expect.isFalse(empty);
+          d.deleteSync(recursive: true);
+          asyncEnd();
+        });
+      });
+  });
+}
+
+void main() {
+  testPauseResumeCancelStream();
+  testStreamIsEmpty();
+}