Specify packageRoot parameter to Isolate.spawnUri.

runtime/lib/isolate_patch.dart

 // Copyright (c) 2012, 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:collection" show HashMap;
 
 patch class ReceivePort {
   /* patch */ factory ReceivePort() = _ReceivePortImpl;
 
   /* patch */ factory ReceivePort.fromRawReceivePort(RawReceivePort rawPort) =
@@ skipping 256 matching lines @@
       return completer.future;
     } catch (e, st) {
       if (readyPort != null) {
         readyPort.close();
       }
       return new Future<Isolate>.error(e, st);
     };
   }
 
   /* patch */ static Future<Isolate> spawnUri(
-      Uri uri, List<String> args, var message, { bool paused: false }) {
+      Uri uri, List<String> args, var message,
+      { bool paused: false, Uri packageRoot }) {
     // `paused` isn't handled yet.
+    // `packageRoot` isn't handled yet.
+    if (packageRoot != null) throw new UnimplementedError("packageRoot");
     RawReceivePort readyPort;
     try {
       // The VM will invoke [_startIsolate] and not `main`.
       readyPort = new RawReceivePort();
       _spawnUri(readyPort.sendPort, uri.toString(), args, message);
       Completer completer = new Completer<Isolate>.sync();
       readyPort.handler = (readyMessage) {
         readyPort.close();
         assert(readyMessage is List);
         assert(readyMessage.length == 2);
@@ skipping 68 matching lines @@
   }
 
   /* patch */ void addErrorListener(SendPort port) {
     throw new UnsupportedError("addErrorListener");
   }
 
   /* patch */ void removeErrorListener(SendPort port) {
     throw new UnsupportedError("removeErrorListener");
   }
 }