Fix a couple type bugs in dart html and what seems like strange type choices in dart:core

sdk/lib/collection/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 dart.collection;
 
 /**
  * Abstract implementation of a list.
  *
  * `ListBase` can be used as a base class for implementing the `List` interface.
@@ skipping 102 matching lines @@
     int length = this.length;
     for (int i = 0; i < length; i++) {
       if (test(this[i])) return true;
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     return false;
   }
 
-  dynamic firstWhere(bool test(E element), { Object orElse() }) {
+  E firstWhere(bool test(E element), { E orElse() }) {
     int length = this.length;
     for (int i = 0; i < length; i++) {
       E element = this[i];
       if (test(element)) return element;
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     if (orElse != null) return orElse();
     throw IterableElementError.noElement();
   }
 
-  dynamic lastWhere(bool test(E element), { Object orElse() }) {
+  E lastWhere(bool test(E element), { E orElse() }) {
     int length = this.length;
     for (int i = length - 1; i >= 0; i--) {
       E element = this[i];
       if (test(element)) return element;
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     if (orElse != null) return orElse();
     throw IterableElementError.noElement();
@@ skipping 348 matching lines @@
       for (E element in iterable) {
         this[index++] = element;
       }
     }
   }
 
   Iterable<E> get reversed => new ReversedListIterable<E>(this);
 
   String toString() => IterableBase.iterableToFullString(this, '[', ']');
 }