Make sure the SSA codegen visit constants used in a switch through the 'visitConstant' method, to e…

tests/language/switch8_test.dart

+// 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.
+
+// Regression test for dart2js that used to not generate code for
+// compile-time constants only seen in case expressions.
+
+class A {
+  const A();
+}
+
+main() {
+  switch (new List(1)[0]) {
+    case const A(): throw 'Test failed';
+  }
+}