Allow Object when doing lookups.

runtime/lib/array.dart

Index: runtime/lib/array.dart
diff --git a/runtime/lib/array.dart b/runtime/lib/array.dart
index cfb640bc01c076d959d31a7d88458025a50cf313..5b87c35654fd851098d33ff69c6fffc150267dbf 100644
--- a/runtime/lib/array.dart
+++ b/runtime/lib/array.dart
@@ -118,7 +118,7 @@ class _ObjectArray<E> implements List<E> {
 
   // Iterable interface.
 
-  bool contains(E element) {
+  bool contains(Object element) {
     return IterableMixinWorkaround.contains(this, element);
   }
 
@@ -371,7 +371,7 @@ class _ImmutableArray<E> implements List<E> {
 
   // Collection interface.
 
-  bool contains(E element) {
+  bool contains(Object element) {
     return IterableMixinWorkaround.contains(this, element);
   }