Add static type warning annotation to make the test pass on analyzer.

tests/language/checked_setter3_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";
 
 bool get inCheckedMode {
   try {
-    String a = 42;
+    var i = 42;
+    String a = i;
   } catch (e) {
     return true;
   }
   return false;
 }
 
 class A<T> {
   T field;
 }
 
@@ skipping 11 matching lines @@
   if (inCheckedMode) {
     Expect.throws(() => a.field = 42, (e) => e is TypeError);
     Expect.throws(() => new B<String>(), (e) => e is TypeError);
     Expect.throws(() => c.field = 'foo', (e) => e is TypeError);
   } else {
     a.field = 42;
     new B<String>();
     c.field = 'foo';
   }
 }