Revert Expando changes. There are checked-mode errors that I need

lib/compiler/implementation/lib/core_patch.dart

Index: lib/compiler/implementation/lib/core_patch.dart
diff --git a/lib/compiler/implementation/lib/core_patch.dart b/lib/compiler/implementation/lib/core_patch.dart
index d6b40ae53bf9456816e879d1505bcf527885e7b8..aea4c6c7c2e0df68062931c651de31cddc668398 100644
--- a/lib/compiler/implementation/lib/core_patch.dart
+++ b/lib/compiler/implementation/lib/core_patch.dart
@@ -14,35 +14,3 @@ patch class Object {
     throw new NoSuchMethodException(this, name, args);
   }
 }
-
-
-// Patch for Expando implementation.
-patch class Expando<T> {
-
-  patch T operator[](Object object) {
-    var values = Primitives.getProperty(object, _EXPANDO_PROPERTY_NAME);
-    return (values === null) ? null : Primitives.getProperty(values, _getKey());
-  }
-
-  patch void operator[]=(Object object, T value) {
-    var values = Primitives.getProperty(object, _EXPANDO_PROPERTY_NAME);
-    if (values === null) {
-      values = new Object();
-      Primitives.setProperty(object, _EXPANDO_PROPERTY_NAME, values);
-    }
-    Primitives.setProperty(values, _getKey(), value);
-  }
-
-  String _getKey() {
-    String key = Primitives.getProperty(this, _KEY_PROPERTY_NAME);
-    if (key === null) {
-      key = "expando\$key\$${_keyCount++}";
-      Primitives.setProperty(this, _KEY_PROPERTY_NAME, key);
-    }
-    return key;
-  }
-
-  static const String _KEY_PROPERTY_NAME = 'expando\$key';
-  static const String _EXPANDO_PROPERTY_NAME = 'expando\$values';
-  static int _keyCount = 0;
-}