Fix for switch type inferrence

tests/compiler/dart2js_extra/12320_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.
+
+import "package:expect/expect.dart";
+
+// Regression test for Issue 12320, Issue 12363.
+
+String log = '';
+int x;
+
+void main() {
+  (run)(run);
+  // The little dance with passing [run] as an argument to confuse the optimizer
+  // so that [run] is not inlined.  If [run] is inlined, the bug (Issue 12320)
+  // eliminates the following 'Expect', making the test appear to pass!
+  Expect.equals('[Foo][Foo 1][Bar][Foo][Foo 0]', log);
+}
+
+void run(f) {
+  if (f is !int) {
+    f(1);
+  } else {
+    x = f;
+    callFoo();
+    x = 2;
+    callBar();
+    callFoo();
+  }
+}
+
+void callFoo() {
+  log += '[Foo]';
+  switch(x) {
+    case 0:
+      log += '[Foo 0]';
+      break;
+    case 1:
+      log += '[Foo 1]';
+      break;
+    default:
+      throw 'invalid x';
+  }
+}
+
+void callBar() {
+  log += '[Bar]';
+  x = 0;
+}