Revert r23577, some unit tests fail.

tests/language/type_propagation_test.dart

Index: tests/language/type_propagation_test.dart
===================================================================
--- tests/language/type_propagation_test.dart	(revision 23577)
+++ tests/language/type_propagation_test.dart	(working copy)
@@ -1,43 +0,0 @@
-// Copyright (c) 2013, 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.
-
-// dart2js used to have an infinite loop in its type propagation
-// algorithm due to types becoming broader instead of narrower.
-
-import "package:expect/expect.dart";
-
-class A {
-  resolveSend(node) {
-    if (node == null) {
-      return [new B()][0];
-    } else {
-      return [new B(), new A()][1];
-    }
-  }
-
-  visitSend(node) {
-    var target = resolveSend(node);
-
-    if (false) {
-      if (false) {
-        target = target.getter;
-        if (false) {
-          target = new Object();
-        }
-      }
-    }
-    return true ? target : null;
-  }
-}
-
-var a = 43;
-
-class B {
-  var getter = a == 42 ? new A() : null;
-}
-
-main() {
-  Expect.isTrue(new A().visitSend(new A()) is A);
-  Expect.isTrue(new A().visitSend(null) is B);
-}