Make IsolateWrapper compatible with the 1.11 isolate API changes.

lib/src/util/isolate_wrapper.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.isolate_wrapper;
 
 import 'dart:async';
 import 'dart:isolate';
 
 import 'io.dart';
 
 // TODO(nweiz): Get rid of this when issue 6610 is fixed.
 /// This is a wrapper around an [Isolate] that supports a callback that will
 /// fire when [Isolate.exit] is called.
 ///
 /// This is necessary to delete the source directory of the isolate only once
 /// the Isolate completes. Note that the callback won't necessarily fire before
 /// the Isolate is killed, but it comes close enough for our purposes.
-class IsolateWrapper implements Isolate {
+///
+/// This avoids implementing Isolate because there's no interface that's
+/// compatible with both Dart before 1.11 and Dart after 1.11.
+class IsolateWrapper {
   final Isolate _inner;
 
   final Function _onExit;
 
   Capability get pauseCapability => _inner.pauseCapability;
   SendPort get controlPort => _inner.controlPort;
   Stream get errors => _inner.errors;
   Capability get terminateCapability => _inner.terminateCapability;
 
   IsolateWrapper(this._inner, this._onExit);
 
   void addErrorListener(SendPort port) => _inner.addErrorListener(port);
   void addOnExitListener(SendPort port) => _inner.addOnExitListener(port);
   Capability pause([Capability resumeCapability]) =>
       _inner.pause(resumeCapability);
-  void ping(SendPort responsePort, [int pingType=Isolate.IMMEDIATE]) =>
-      _inner.ping(responsePort, pingType);
+  void ping(SendPort responsePort) => _inner.ping(responsePort);
   void removeErrorListener(SendPort port) => _inner.removeErrorListener(port);
   void removeOnExitListener(SendPort port) => _inner.removeOnExitListener(port);
   void resume(Capability resumeCapability) => _inner.resume(resumeCapability);
   void setErrorsFatal(bool errorsAreFatal) =>
       _inner.setErrorsFatal(errorsAreFatal);
   String toString() => _inner.toString();
 
-  void kill([int priority=Isolate.BEFORE_NEXT_EVENT]) {
-    if (supportsIsolateKill) _inner.kill(priority);
+  void kill() {
+    if (supportsIsolateKill) _inner.kill();
     _onExit();
   }
 }