Allow Object when doing lookups.

sdk/lib/core/uri.dart

Index: sdk/lib/core/uri.dart
diff --git a/sdk/lib/core/uri.dart b/sdk/lib/core/uri.dart
index c0a7fdf9f5d2d3623c816a15d502116374085a00..941069117f39574fc0a6f803332e88e516722120 100644
--- a/sdk/lib/core/uri.dart
+++ b/sdk/lib/core/uri.dart
@@ -1016,9 +1016,9 @@ class _UnmodifiableMap<K, V> implements Map<K, V> {
   final Map _map;
   const _UnmodifiableMap(this._map);
 
-  bool containsValue(V value) => _map.containsValue(value);
-  bool containsKey(K key) => _map.containsKey(key);
-  V operator [](K key) => _map[key];
+  bool containsValue(Object value) => _map.containsValue(value);
+  bool containsKey(Object key) => _map.containsKey(key);
+  V operator [](Object key) => _map[key];
   void operator []=(K key, V value) {
     throw new UnsupportedError("Cannot modify an unmodifiable map");
   }
@@ -1028,7 +1028,7 @@ class _UnmodifiableMap<K, V> implements Map<K, V> {
   addAll(Map other) {
     throw new UnsupportedError("Cannot modify an unmodifiable map");
   }
-  V remove(K key) {
+  V remove(Object key) {
     throw new UnsupportedError("Cannot modify an unmodifiable map");
   }
   void clear() {