Fix top-level inference errors for most of the newly failing tests.

tests/language_strong/closure_in_field_initializer_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";
 
 class Foo {
   var closures = {
-    'a': (x, y) => x + y
+    'a': (int x, int y) => x + y
   };
 }
 
 main() {
   var closures = new Foo().closures;
   Expect.equals(6, closures['a'](4, 2));
 }