Fix bug in SsaConstructionFieldTypes: handle mulitple assignments to the same field.

tests/language/compiler_annotations.dart

Index: tests/language/compiler_annotations.dart
===================================================================
--- tests/language/compiler_annotations.dart	(revision 0)
+++ tests/language/compiler_annotations.dart	(revision 0)
@@ -0,0 +1,12 @@
+// 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.
+
+library compiler_annotations;
+
+// This library contains annotations useful for testing.
+
+// TODO(ngeoffray): Implement in dart2js.
+class DontInline {
+  const DontInline();
+}