Allow Object when doing lookups.

sdk/lib/_collection_dev/iterable.dart

Index: sdk/lib/_collection_dev/iterable.dart
diff --git a/sdk/lib/_collection_dev/iterable.dart b/sdk/lib/_collection_dev/iterable.dart
index a6a65b2096be9f464f02c67003decdce7f2b6caf..bd93109ffd8ba1d23deb2e9521ed2d8efb93b42c 100644
--- a/sdk/lib/_collection_dev/iterable.dart
+++ b/sdk/lib/_collection_dev/iterable.dart
@@ -46,7 +46,7 @@ abstract class ListIterable<E> extends IterableBase<E> {
     return elementAt(0);
   }
 
-  bool contains(E element) {
+  bool contains(Object element) {
     int length = this.length;
     for (int i = 0; i < length; i++) {
       if (elementAt(i) == element) return true;
@@ -608,7 +608,7 @@ class EmptyIterable<E> extends IterableBase<E> {
 
   E elementAt(int index) { throw new RangeError.value(index); }
 
-  bool contains(E element) => false;
+  bool contains(Object element) => false;
 
   bool every(bool test(E element)) => true;