fixes to polymer, gets tests back to a stable state

pkg/observe/lib/src/dirty_check.dart

 // Copyright (c) 2013, 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.
 
 /**
  * *Warning*: this library is **internal**, and APIs are subject to change.
  *
  * Tracks observable objects for dirty checking and testing purposes.
  *
  * It can collect all observed objects, which can be used to trigger predictable
  * delivery of all pending changes in a test, including objects allocated
  * internally to another library, such as those in `package:mdv`.
  */
 library observe.src.dirty_check;
 
+import 'dart:async';
 import 'package:logging/logging.dart';
 import 'package:observe/observe.dart' show Observable;
 
 /** The number of active observables in the system. */
 int get allObservablesCount => _allObservablesCount;
 
 int _allObservablesCount = 0;
 
 List<Observable> _allObservables = null;
 
@@ skipping 51 matching lines @@
           '${info[0]}, object: ${info[1]}.');
     }
   }
 
   _allObservablesCount = _allObservables.length;
   _delivering = false;
 }
 
 const MAX_DIRTY_CHECK_CYCLES = 1000;
 
-
 /**
  * Log for messages produced at runtime by this library. Logging can be
  * configured by accessing Logger.root from the logging library.
  */
 final Logger _logger = new Logger('Observable.dirtyCheck');
+
+/**
+ * Creates a [ZoneSpecification] to set up automatic dirty checking after each
+ * batch of async operations. This ensures that change notifications are always
+ * delivered. Typically used via [dirtyCheckZone].
+ */
+ZoneSpecification dirtyCheckZoneSpec() {
+  bool pending = false;
+
+  enqueueDirtyCheck(ZoneDelegate parent, Zone zone) {
+    // Only schedule one dirty check per microtask.
+    if (pending) return;
+
+    pending = true;
+    parent.scheduleMicrotask(zone, () {
+      pending = false;
+      Observable.dirtyCheck();
+    });
+  }
+
+  wrapCallback(Zone self, ZoneDelegate parent, Zone zone, f()) {
+    // TODO(jmesserly): why does this happen?
+    if (f == null) return f;
+    return () {
+      enqueueDirtyCheck(parent, zone);
+      return f();
+    };
+  }
+
+  wrapUnaryCallback(Zone self, ZoneDelegate parent, Zone zone, f(x)) {
+    // TODO(jmesserly): why does this happen?
+    if (f == null) return f;
+    return (x) {
+      enqueueDirtyCheck(parent, zone);
+      return f(x);
+    };
+  }
+
+  return new ZoneSpecification(
+      registerCallback: wrapCallback,
+      registerUnaryCallback: wrapUnaryCallback);
+}
+
+/**
+ * Forks a [Zone] off the current one that does dirty-checking automatically
+ * after each batch of async operations. Equivalent to:
+ *
+ *     Zone.current.fork(specification: dirtyCheckZoneSpec());
+ */
+Zone dirtyCheckZone() => Zone.current.fork(specification: dirtyCheckZoneSpec());