Allow Object when doing lookups.

sdk/lib/_collection_dev/list.dart

Index: sdk/lib/_collection_dev/list.dart
diff --git a/sdk/lib/_collection_dev/list.dart b/sdk/lib/_collection_dev/list.dart
index 90a1d1643f200a62bb4ead6893c883ae5a02fd6a..7f894bb65fb748a262b913c8d3e6b1734f4d125d 100644
--- a/sdk/lib/_collection_dev/list.dart
+++ b/sdk/lib/_collection_dev/list.dart
@@ -35,7 +35,7 @@ abstract class FixedLengthListMixin<E>  {
         "Cannot add to a fixed-length list");
   }
 
-  bool remove(E element) {
+  bool remove(Object element) {
     throw new UnsupportedError(
         "Cannot remove from a fixed-length list");
   }
@@ -130,7 +130,7 @@ abstract class UnmodifiableListMixin<E> {
         "Cannot add to an unmodifiable list");
   }
 
-  bool remove(E element) {
+  bool remove(Object element) {
     throw new UnsupportedError(
         "Cannot remove from an unmodifiable list");
   }
@@ -239,7 +239,7 @@ class ListMapView<E> implements Map<int, E> {
 
   bool get isEmpty => _values.isEmpty;
   bool get isNotEmpty => _values.isNotEmpty;
-  bool containsValue(E value) => _values.contains(value);
+  bool containsValue(Object value) => _values.contains(value);
   bool containsKey(int key) => key is int && key >= 0 && key < length;
 
   void forEach(void f(int key, E value)) {