Make Directory.list pull-based, making it possible to pause, resume and cancel directory listing.

tests/standalone/io/directory_list_pause_test.dart

Index: tests/standalone/io/directory_list_pause_test.dart
diff --git a/tests/standalone/io/directory_list_pause_test.dart b/tests/standalone/io/directory_list_pause_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..86ff1566d87a6979dbc1b0fb6c46840853505674
--- /dev/null
+++ b/tests/standalone/io/directory_list_pause_test.dart
@@ -0,0 +1,44 @@
+// 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";
+import "dart:async";
+import "dart:io";
+import "dart:isolate";
+
+
+void testPauseList() {
+  var keepAlive = new ReceivePort();
+  new Directory("").createTemp().then((d) {
+    // Linux reads 2K at a time.
+    int total = 2 * 1024 + 1;
+    for (int i = 0; i < total; i++) {
+      new File("${d.path}/$i").createSync();
+    }
+    bool first = true;
+    var subscription;
+    int count = 0;
+    subscription = d.list().listen((file) {
+      if (first) {
+        first = false;
+        subscription.pause();
+        Timer.run(() {
+          for (int i = 0; i < total; i++) {
+            new File("${d.path}/$i").deleteSync();
+          }
+          subscription.resume();
+        });
+      }
+      count++;
+    }, onDone: () {
+      Expect.isTrue(count < total);
+      keepAlive.close();
+      d.delete().then((ignore) => keepAlive.close());
+    });
+  });
+}
+
+void main() {
+  testPauseList();
+}