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

runtime/lib/errors_patch.dart

Index: runtime/lib/errors_patch.dart
diff --git a/runtime/lib/errors_patch.dart b/runtime/lib/errors_patch.dart
index f26d4d4e238feb6c54a9618a043040da2ff5bd8e..595f6f8620bcde3ab34e253f191b7a08fa6cdd59 100644
--- a/runtime/lib/errors_patch.dart
+++ b/runtime/lib/errors_patch.dart
@@ -395,3 +395,21 @@ class _CompileTimeError extends Error {
   _CompileTimeError(this._errorMsg);
   String toString() => _errorMsg;
 }
+
+dynamic _classRangeAssert(int position, dynamic instance, _Type type, int cid,
+    int lowerLimit, int upperLimit) {
+  if ((cid < lowerLimit || cid > upperLimit) && instance != null) {
+    _TypeError._throwNew(position, instance, type, " in type cast", null);
+  }
+
+  return instance;
+}
+
+dynamic _classIdEqualsAssert(
+    int position, dynamic instance, _Type type, int cid, int otherCid) {
+  if (cid != otherCid && instance != null) {
+    _TypeError._throwNew(position, instance, type, " in type cast", null);
+  }
+
+  return instance;
+}