unfork DDC's copy of most SDK libraries

pkg/dev_compiler/tool/input_sdk/lib/core/identical.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-part of dart.core;
-
-/**
- * Check whether two references are to the same object.
- */
-external bool identical(Object a, Object b);
-
-/**
- * Returns the identity hash code of `object`.
- *
- * Returns the same value as `object.hashCode` if [object] has not overridden
- * [Object.hashCode]. Returns the value that [Object.hashCode] would return
- * on this object, even if `hashCode` has been overridden.
- *
- * This hash code is compatible with [identical].
- */
-external int identityHashCode(Object object);