Support for type dynamic in VM

tests/language/cast_test.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.
 // Dart test program for constructors and initializers.
 
 // Test 'expression as Type' casts.
 
 class C {
   final int foo = 42;
 }
@@ skipping 24 matching lines @@
   Expect.equals(37, ((od as C) as D).bar);
   (oc as D).foo;  /// 01: runtime error
   (on as D).toString();
   (on as D).foo;  /// 02: runtime error
   (on as C).foo;  /// 03: runtime error
   oc.foo;  /// 04: static type warning
   od.foo;  /// 05: static type warning
   (on as Object).toString();
   (oc as Object).toString();
   (od as Object).toString();
-  (on as Dynamic).toString();
-  (on as Dynamic).foo;  /// 07: runtime error
-  (oc as Dynamic).foo;
-  (od as Dynamic).foo;
-  (oc as Dynamic).bar;  /// 08: runtime error
-  (od as Dynamic).bar;
+  (on as dynamic).toString();
+  (on as dynamic).foo;  /// 07: runtime error
+  (oc as dynamic).foo;
+  (od as dynamic).foo;
+  (oc as dynamic).bar;  /// 08: runtime error
+  (od as dynamic).bar;
   C c = oc as C;
   c = od as C;
   c = oc;
   D d = od as D;
   d = oc as D;  /// 10: runtime error
   d = od;
 
   (ol as List)[0];
   (ol as List<int>)[0];
-  (ol as Dynamic)[0];
+  (ol as dynamic)[0];
   (ol as String).length;  /// 12: runtime error
   int x = (ol as List<int>)[0];
   (ol as List<int>)[0] = (oi as int);
 
   (os as String).length;
-  (os as Dynamic).length;
+  (os as dynamic).length;
   (oi as String).length;  /// 13: runtime error
   (os as List).length;  /// 14: runtime error
 
   (oi as int) + 2;
   (oi as List).length;  /// 15: runtime error
 }