Fix VM implementation of CastError not to extend TypeError (issue 5280).

tests/standalone/assert_test.dart

 // Copyright (c) 2011, 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.
 // VMOptions=--enable_asserts
+
 // Dart test program testing assert statements.
+
 import "package:expect/expect.dart";
 
 class AssertTest {
   static test() {
     try {
       assert(false);
       Expect.fail("Assertion 'false' didn't fail.");
-    } on AssertionError catch (error) {
-      Expect.equals("false", error.failedAssertion);
-      int pos = error.url.lastIndexOf("/", error.url.length);
-      if (pos == -1) {
-        pos = error.url.lastIndexOf("\\", error.url.length);
-      }
-      String subs = error.url.substring(pos + 1, error.url.length);
-      Expect.equals("assert_test.dart", subs);
-      Expect.equals(11, error.line);
-      Expect.equals(14, error.column);
+    } on AssertionError catch (error, stacktrace) {
+      Expect.isTrue(error.toString().contains("'false'"));
+      Expect.isTrue(stacktrace.toString().contains("assert_test.dart:13:14"));
     }
   }
   static testClosure() {
     try {
       assert(() => false);
       Expect.fail("Assertion '() => false' didn't fail.");
-    } on AssertionError catch (error) {
-      Expect.equals("() => false", error.failedAssertion);
-      int pos = error.url.lastIndexOf("/", error.url.length);
-      if (pos == -1) {
-        pos = error.url.lastIndexOf("\\", error.url.length);
-      }
-      String subs = error.url.substring(pos + 1, error.url.length);
-      Expect.equals("assert_test.dart", subs);
-      Expect.equals(27, error.line);
-      Expect.equals(14, error.column);
+    } on AssertionError catch (error, stacktrace) {
+      Expect.isTrue(error.toString().contains("'() => false'"));
+      Expect.isTrue(stacktrace.toString().contains("assert_test.dart:22:14"));
     }
   }
 
   static testMain() {
     test();
     testClosure();
   }
 }
 
 main() {
   AssertTest.testMain();
 }