Run dartfmt on kernel package

pkg/kernel/testcases/closures/for_variable_capture_test.dart

 // Copyright (c) 2016, 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.
 
 main() {
   var closure;
-  for (var i=0, fn = () => i; i < 3; i++) {
+  for (var i = 0, fn = () => i; i < 3; i++) {
     i += 1;
     closure = fn;
   }
   var x = closure();
   if (x != 1) {
     throw "Expected 1, but got $x.";
   }
 }