Don't restrict type on Setlet.remove.

dart/pkg/compiler/lib/src/util/setlet.dart

Index: dart/pkg/compiler/lib/src/util/setlet.dart
diff --git a/dart/pkg/compiler/lib/src/util/setlet.dart b/dart/pkg/compiler/lib/src/util/setlet.dart
index 10c0224487c73b80b0b6ca0b14cccf7e18323bec..f497561ecf43c4e6c48300b6a4a4eab52ee78d53 100644
--- a/dart/pkg/compiler/lib/src/util/setlet.dart
+++ b/dart/pkg/compiler/lib/src/util/setlet.dart
@@ -157,7 +157,7 @@ class Setlet<E> extends IterableBase<E> implements Set<E> {
     }
   }
 
-  bool remove(E element) {
+  bool remove(Object element) {
     if (_extra == null) {
       if (_contents == element) {
         _contents = _MARKER;