Cleanup inconsistent dart:html method signatures

sdk/lib/html/html_common/css_class_set.dart

Index: sdk/lib/html/html_common/css_class_set.dart
diff --git a/sdk/lib/html/html_common/css_class_set.dart b/sdk/lib/html/html_common/css_class_set.dart
index 4d7de3bcea9f07933c2fcf168f2d9868357bfe7c..5704bfa91a39c69d00df2bd42a784d3929a4a4bf 100644
--- a/sdk/lib/html/html_common/css_class_set.dart
+++ b/sdk/lib/html/html_common/css_class_set.dart
@@ -130,7 +130,7 @@ abstract class CssClassSetImpl implements CssClassSet {
    * This is the Dart equivalent of jQuery's
    * [removeClass](http://api.jquery.com/removeClass/).
    */
-  void removeAll(Iterable<String> iterable) {
+  void removeAll(Iterable<Object> iterable) {
     modify((s) => s.removeAll(iterable));
   }
 
@@ -148,7 +148,7 @@ abstract class CssClassSetImpl implements CssClassSet {
     iterable.forEach((e) => toggle(e, shouldAdd));
   }
 
-  void retainAll(Iterable<String> iterable) {
+  void retainAll(Iterable<Object> iterable) {
     modify((s) => s.retainAll(iterable));
   }
 
@@ -160,10 +160,10 @@ abstract class CssClassSetImpl implements CssClassSet {
     modify((s) => s.retainWhere(test));
   }
 
-  bool containsAll(Iterable<String> collection) =>
+  bool containsAll(Iterable<Object> collection) =>
     readClasses().containsAll(collection);
 
-  Set<String> intersection(Set<String> other) =>
+  Set<String> intersection(Set<Object> other) =>
     readClasses().intersection(other);
 
   Set<String> union(Set<String> other) =>