Add support for micro-tasks in Dartium.

tools/dom/src/native_DOMImplementation.dart

Index: tools/dom/src/native_DOMImplementation.dart
diff --git a/tools/dom/src/native_DOMImplementation.dart b/tools/dom/src/native_DOMImplementation.dart
index 2c82dddb7592a1dcc8261af5a4dfba4a184b1459..e6b5c15c3a1949b65e7f0dde61d0408bcc176b43 100644
--- a/tools/dom/src/native_DOMImplementation.dart
+++ b/tools/dom/src/native_DOMImplementation.dart
@@ -411,6 +411,20 @@ get _pureIsolateTimerFactoryClosure =>
   throw new UnimplementedError("Timers on background isolates "
                                "are not supported in the browser"));
 
+final _enqueueImmediateHelperNode = new DivElement();
+get _enqueueImmediateFactoryClosure => (void callback()) {
+  new MutationObserver((changes, observer) {
+    observer.disconnect();
+    callback();
+  }).observe(_enqueueImmediateHelperNode, childList: true, attributes: true);
+  _enqueueImmediateHelperNode.attributes.clear();

[blois, 2013/10/03 16:54:29]

The attributes getter isn't as lightweight as it should be, a better trigger
which we use in dart:html right now is:

_enqueueImmediateHelperNode.hidden = !_enqueueImmediateHelperNode.hidden;

Also seems like the MutationObserver itself should be cached and reused. See:
https://code.google.com/p/dart/source/browse/branches/bleeding_edge/dart/tool...

[Anders Johnsen, 2013/10/10 14:48:54]

Done.

+  _enqueueImmediateHelperNode.attributes["text"] = " ";
+};
+
+get _pureIsolateEnqueueImmediateFactoryClosure => ((void callback()) =>
+  throw new UnimplementedError("runAsync in background isolates "
+                               "are not supported in the browser"));
+
 void _initializeCustomElement(Element e) {
   _Utils.initializeCustomElement(e);
 }