Set.add returns true if item has been added, otherwise false

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 1e2dce72f800d62f4e7211bb921c7ff5c99e2424..a81497e401f08207a316f332de3962bba0dc4049 100644
--- a/sdk/lib/html/html_common/css_class_set.dart
+++ b/sdk/lib/html/html_common/css_class_set.dart
@@ -92,10 +92,10 @@ abstract class CssClassSetImpl implements CssClassSet {
    * This is the Dart equivalent of jQuery's
    * [addClass](http://api.jquery.com/addClass/).
    */
-  void add(String value) {
+  bool add(String value) {
     // TODO - figure out if we need to do any validation here
     // or if the browser natively does enough.
-    modify((s) => s.add(value));
+    return modify((s) => s.add(value));
   }
 
   /**
@@ -206,10 +206,11 @@ abstract class CssClassSetImpl implements CssClassSet {
    *   After f returns, the modified set is written to the
    *       className property of this element.
    */
-  void modify( f(Set<String> s)) {
+  modify( f(Set<String> s)) {
     Set<String> s = readClasses();
-    f(s);
+    var ret = f(s);
     writeClasses(s);
+    return ret;
   }
 
   /**