Support Dart 1.8.0.

lib/src/isolate_wrapper.dart

Index: lib/src/isolate_wrapper.dart
diff --git a/lib/src/isolate_wrapper.dart b/lib/src/isolate_wrapper.dart
index e869311585900a7e54bcbd0b1e474874062205e9..f0031da01c8dccb7dcc9b452819191d2b4e3ef1c 100644
--- a/lib/src/isolate_wrapper.dart
+++ b/lib/src/isolate_wrapper.dart
@@ -7,6 +7,8 @@ library unittest.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.
@@ -40,7 +42,7 @@ class IsolateWrapper implements Isolate {
   String toString() => _inner.toString();
 
   void kill([int priority=Isolate.BEFORE_NEXT_EVENT]) {
-    _inner.kill(priority);
+    if (supportsIsolateKill) _inner.kill(priority);
     _onExit();
   }
 }