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

sdk/lib/html/html_common/css_class_set.dart

 // Copyright (c) 2012, 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 html_common;
 
 abstract class CssClassSetImpl implements CssClassSet {
 
   String toString() {
     return readClasses().join(' ');
@@ skipping 63 matching lines @@
   }
   // interface Collection - END
 
   // interface Set - BEGIN
   /**
    * Determine if this element contains the class [value].
    *
    * This is the Dart equivalent of jQuery's
    * [hasClass](http://api.jquery.com/hasClass/).
    */
-  bool contains(String value) => readClasses().contains(value);
+  bool contains(Object value) => readClasses().contains(value);
 
   /** Lookup from the Set interface. Not interesting for a String set. */
-  String lookup(String value) => contains(value) ? value : null;
+  String lookup(Object value) => contains(value) ? value : null;
 
   /**
    * Add the class [value] to element.
    *
    * This is the Dart equivalent of jQuery's
    * [addClass](http://api.jquery.com/addClass/).
    */
   bool add(String value) {
     // TODO - figure out if we need to do any validation here
     // or if the browser natively does enough.
@@ skipping 79 matching lines @@
   String get single => readClasses().single;
   List<String> toList({ bool growable: true }) =>
       readClasses().toList(growable: growable);
   Set<String> toSet() => readClasses().toSet();
   Iterable<String> take(int n) => readClasses().take(n);
   Iterable<String> takeWhile(bool test(String value)) =>
       readClasses().takeWhile(test);
   Iterable<String> skip(int n) => readClasses().skip(n);
   Iterable<String> skipWhile(bool test(String value)) =>
       readClasses().skipWhile(test);
-  dynamic firstWhere(bool test(String value), { Object orElse() }) =>
+  String firstWhere(bool test(String value), { String orElse() }) =>
       readClasses().firstWhere(test, orElse: orElse);
-  dynamic lastWhere(bool test(String value), { Object orElse()}) =>
+  String lastWhere(bool test(String value), { String orElse()}) =>
       readClasses().lastWhere(test, orElse: orElse);
   String singleWhere(bool test(String value)) =>
       readClasses().singleWhere(test);
   String elementAt(int index) => readClasses().elementAt(index);
 
   void clear() {
     modify((s) => s.clear());
   }
   // interface Set - END
 
@@ skipping 20 matching lines @@
    */
   Set<String> readClasses();
 
   /**
    * Join all the elements of a set into one string and write
    * back to the element.
    * This is intended to be overridden by specific implementations.
    */
   void writeClasses(Set<String> s);
 }