Working implementation of #29153 range check in as-casts.

runtime/lib/errors_patch.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.
 
 @patch
 class Error {
   @patch
   static String _objectToString(Object object) {
     return Object._toString(object);
   }
@@ skipping 377 matching lines @@
 
     return msg_buf.toString();
   }
 }
 
 class _CompileTimeError extends Error {
   final String _errorMsg;
   _CompileTimeError(this._errorMsg);
   String toString() => _errorMsg;
 }
+
+dynamic _classRangeAssert(int position, String InTypeCast, dynamic instance,
+    _Type type, int cid, int lowerLimit, int upperLimit) {
+  if ((cid < lowerLimit || cid > upperLimit) && instance != null) {
+    _TypeError._throwNew(0, instance, type, InTypeCast, "");

[rmacnak, 2017/04/10 21:07:23]

0 -> position.

It's safe to say "in type type" here. The string literal will be canonicalized
to the same object as the predefined symbol.

+  }
+
+  return instance;
+}
+
+dynamic _classIdEqualsAssert(int position, String InTypeCast, dynamic instance,
+    _Type type, int cid, int otherCid) {
+  if (cid != otherCid && instance != null) {
+    _TypeError._throwNew(0, instance, type, InTypeCast, "");
+  }
+
+  return instance;
+}