Make List.remove return boolean.

sdk/lib/html/html_common/filtered_element_list.dart

Index: sdk/lib/html/html_common/filtered_element_list.dart
diff --git a/sdk/lib/html/html_common/filtered_element_list.dart b/sdk/lib/html/html_common/filtered_element_list.dart
index 0efe3d540deb0e1d008a30cd66274d0e6c0831f7..a1ff58cd08c66f666d08f93175355ff448d284e1 100644
--- a/sdk/lib/html/html_common/filtered_element_list.dart
+++ b/sdk/lib/html/html_common/filtered_element_list.dart
@@ -120,15 +120,16 @@ class FilteredElementList extends ListBase<Element> {
     return result;
   }
 
-  void remove(Object element) {
+  bool remove(Object element) {
     if (element is! Element) return;
     for (int i = 0; i < length; i++) {
       Element indexElement = this[i];
       if (identical(indexElement, element)) {
         indexElement.remove();
-        return;
+        return true;
       }
     }
+    return false;
   }