for discussion: support for zones in DOM events

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 bea3fc24b1ef6f245b169b59bc1eed7ffa415881..655aefda5b4a313aeb5d80b908c980320e5050a0 100644
--- a/sdk/lib/async/zone.dart
+++ b/sdk/lib/async/zone.dart
@@ -130,6 +130,11 @@ abstract class _Zone {
    * This usually means that the [child] has finished executing and is done.
    */
   void _removeChild(_Zone child);
+
+  /**
+   * True if this is the default zone, otherwise false.
+   */
+  bool get isDefault;
 }
 
 /**
@@ -157,6 +162,8 @@ class _ZoneBase implements _Zone {
     assert(this is _DefaultZone);
   }
 
+  bool get isDefault => false;
+
   _Zone get _errorZone => _parentZone._errorZone;
 
   void handleUncaughtError(error) {
@@ -321,6 +328,8 @@ class _ZoneBase implements _Zone {
 class _DefaultZone extends _ZoneBase {
   _DefaultZone() : super._defaultZone();
 
+  bool get isDefault => true;
+
   _Zone get _errorZone => this;
 
   handleUncaughtError(error) {
@@ -556,3 +565,16 @@ runZonedExperimental(body(),
   _CatchErrorsZone zone = new _CatchErrorsZone(_Zone._current, onError, onDone);
   return zone.runWaitForCompletion(body);
 }
+
+/**
+ * Gets the current zone. See [runZonedExperimental].
+ *
+ * *Warning*: all Zone APIs are subject to change. Your code may break in the
+ * future with [NoSuchMethodError] or cause have other unexpected behavior.
+ */
+// TODO(jmesserly): how do we expose only the features that dart:html needs?
+// Crazy idea: move EventStreamSubscription to be an abstract base class in
+// dart:async (possibly renaming it) and make the calls to add and remove the
+// listener abstract. Then dart:html overrides it to use DOM addEventListener
+// and removeEventListener.
+get currentZoneExperimental => _Zone.current;