Very simple version of Isolates.

sdk/lib/async/zone.dart

Index: sdk/lib/async/zone.dart
diff --git a/sdk/lib/async/zone.dart b/sdk/lib/async/zone.dart
index 2306a6e646a72f38d4af7130ac73861ab4b9cc83..297f83ff4ccb21c7c61e7fa9f9e4a2aa61cd19d7 100644
--- a/sdk/lib/async/zone.dart
+++ b/sdk/lib/async/zone.dart
@@ -701,16 +701,18 @@ class _CustomizedZone extends _BaseZone {
 
 void _rootHandleUncaughtError(
     Zone self, ZoneDelegate parent, Zone zone, error, StackTrace stackTrace) {
-  _scheduleAsyncCallback(() {
-    print("Uncaught Error: ${error}");
-    var trace = stackTrace;
-    if (trace == null) trace = getAttachedStackTrace(error);
-    // Clear the attached stack trace (if any).
-    _attachStackTrace(error, null);
-    if (trace != null) {
-      print("Stack Trace: \n$trace\n");
-    }
-    throw error;
+  self.run(() {
+    _scheduleAsyncCallback(() {
+      print("Uncaught Error: ${error}");
+      var trace = stackTrace;
+      if (trace == null) trace = getAttachedStackTrace(error);
+      // Clear the attached stack trace (if any).
+      _attachStackTrace(error, null);
+      if (trace != null) {
+        print("Stack Trace: \n$trace\n");
+      }
+      throw error;
+    });
   });
 }
 
@@ -849,6 +851,14 @@ class _RootZone extends _BaseZone {
 
   operator [](Symbol key) => null;
 
+  dynamic runUnaryGuarded(f, arg) {
+    try {
+      return runUnary(f, arg);
+    } catch (e, s) {
+      return handleUncaughtError(e, s);
+    }
+  }
+
   // Methods that can be customized by the zone specification.
 
   dynamic handleUncaughtError(error, StackTrace stackTrace) =>