Expose PhantomJS's remote debugger URL.

lib/src/util/io.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.
 
 library test.util.io;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:mirrors';
@@ skipping 190 matching lines @@
 ///
 /// [tryPort] should return a non-`null` value or a Future completing to a
 /// non-`null` value once it binds successfully. This value will be returned
 /// by [getUnusedPort] in turn.
 ///
 /// This is necessary for ensuring that our port binding isn't flaky for
 /// applications that don't print out the bound port.
 Future getUnusedPort(tryPort(int port)) {
   var value;
   return Future.doWhile(() async {
-    var socket = await RawServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0);
-    var port = socket.port;
-    await socket.close();
-
-    value = await tryPort(port);
+    value = await tryPort(await getUnsafeUnusedPort());
     return value == null;
   }).then((_) => value);
 }
+
+/// Returns a port that is probably, but not definitely, not in use.
+///
+/// This has a built-in race condition: another process may bind this port at
+/// any time after this call has returned. If at all possible, callers should
+/// use [getUnusedPort] instead.
+Future<int> getUnsafeUnusedPort() async {
+  var socket = await RawServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0);
+  var port = socket.port;
+  await socket.close();
+  return port;
+}