workaround for event handlers: don't return StreamSubscription as model

pkg/observe/lib/src/path_observer.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.
 
 library observe.src.path_observer;
 
 import 'dart:async';
 @MirrorsUsed(metaTargets: const [Reflectable, ObservableProperty],
     override: 'observe.src.path_observer')
 import 'dart:mirrors';
@@ skipping 316 matching lines @@
     final member = type.declarations[name];
     if (member is MethodMirror && member.isRegularMethod) return true;
     type = _safeSuperclass(type);
   }
   return false;
 }
 
 ClassMirror _safeSuperclass(ClassMirror type) {
   try {
     return type.superclass;
-  } on UnsupportedError catch (e) {
-    // TODO(jmesserly): dart2js throws this error when the type is not
+  } /*on UnsupportedError*/ catch (e) {
+    // Note: dart2js throws UnsupportedError when the type is not
     // reflectable.
+    // TODO(jmesserly): dart2js also throws a NoSuchMethodError if the `type` is
+    // a bound generic, because they are not fully implemented. See
+    // https://code.google.com/p/dart/issues/detail?id=15573
     return objectType;
   }
 }
 
 // From: https://github.com/rafaelw/ChangeSummary/blob/master/change_summary.js
 
 final _pathRegExp = () {
   const identStart = '[\$_a-zA-Z]';
   const identPart = '[\$_a-zA-Z0-9]';
   const ident = '$identStart+$identPart*';
   const elementIndex = '(?:[0-9]|[1-9]+[0-9]+)';
   const identOrElementIndex = '(?:$ident|$elementIndex)';
   const path = '(?:$identOrElementIndex)(?:\\.$identOrElementIndex)*';
   return new RegExp('^$path\$');
 }();
 
 final _spacesRegExp = new RegExp(r'\s');
 
 bool _isPathValid(String s) {
   s = s.replaceAll(_spacesRegExp, '');
 
   if (s == '') return true;
   if (s[0] == '.') return false;
   return _pathRegExp.hasMatch(s);
 }
 
 final Logger _logger = new Logger('observe.PathObserver');