add @MirrorsUsed to observe/polymer/polymer_exprs pkgs

pkg/observe/lib/src/observable_list.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.
 
 part of observe;
 
 /**
  * Represents an observable list of model values. If any items are added,
  * removed, or replaced, then observers that are listening to [changes]
  * will be notified.
@@ skipping 16 matching lines @@
   ObservableList([int length])
       : _list = length != null ? new List<E>(length) : <E>[];
 
   /**
    * Creates an observable list with the elements of [other]. The order in
    * the list will be the order provided by the iterator of [other].
    */
   factory ObservableList.from(Iterable<E> other) =>
       new ObservableList<E>()..addAll(other);
 
-  int get length => _list.length;
+  @reflectable int get length => _list.length;
 
-  set length(int value) {
+  @reflectable set length(int value) {
     int len = _list.length;
     if (len == value) return;
 
     // Produce notifications if needed
     if (hasObservers) {
       if (value < len) {
         // Remove items, then adjust length. Note the reverse order.
         _recordChange(new ListChangeRecord(value, removedCount: len - value));
       } else {
         // Adjust length then add items
         _recordChange(new ListChangeRecord(len, addedCount: value - len));
       }
     }
 
     _list.length = value;
   }
 
-  E operator [](int index) => _list[index];
+  @reflectable E operator [](int index) => _list[index];
 
-  void operator []=(int index, E value) {
+  @reflectable void operator []=(int index, E value) {
     var oldValue = _list[index];
     if (hasObservers) {
       _recordChange(new ListChangeRecord(index, addedCount: 1,
                                                 removedCount: 1));
     }
     _list[index] = value;
   }
 
   // The following methods are here so that we can provide nice change events.
 
@@ skipping 201 matching lines @@
 
       if (added > 0 || removed > 0) {
         notifyChange(new ListChangeRecord(startIndex, addedCount: added,
             removedCount: removed));
       }
 
       offset += removed - added;
     }
   }
 }