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

sdk/lib/internal/iterable.dart

 // Copyright (c) 2011, 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._internal;
 
 /**
  * Marker interface for [Iterable] subclasses that have an efficient
  * [length] implementation.
  */
@@ skipping 76 matching lines @@
     int length = this.length;
     for (int i = 0; i < length; i++) {
       if (test(elementAt(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 = elementAt(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 = elementAt(i);
       if (test(element)) return element;
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     if (orElse != null) return orElse();
     throw IterableElementError.noElement();
@@ skipping 1039 matching lines @@
  * Creates errors throw by [Iterable] when the element count is wrong.
  */
 abstract class IterableElementError {
   /** Error thrown thrown by, e.g., [Iterable.first] when there is no result. */
   static StateError noElement() => new StateError("No element");
   /** Error thrown by, e.g., [Iterable.single] if there are too many results. */
   static StateError tooMany() => new StateError("Too many elements");
   /** Error thrown by, e.g., [List.setRange] if there are too few elements. */
   static StateError tooFew() => new StateError("Too few elements");
 }