dart2js: run dartfmt on tests

tests/compiler/dart2js_extra/compound_operator_index_test.dart

 // Copyright (c) 2012, 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 A {
   List<int> list;
   A(int a, int b) : list = <int>[a, b];
   operator [](index) => list[index];
@@ skipping 25 matching lines @@
     trace.add(value);
     this.value = this.value + 1;
     return this;
   }
 }
 
 B getB(trace) {
   trace.add(-1);
   return new B(trace);
 }
+
 int getIndex(trace) {
   trace.add(-2);
   return 42;
 }
 
 main() {
   A a = new A(1, 2);
   Expect.equals(1, a[0]);
   Expect.equals(2, a[1]);
 
@@ skipping 10 matching lines @@
   Expect.equals(1, a[0]);
 
   a[0] += 2;
   Expect.equals(3, a[0]);
 
   List trace = new List();
   getB(trace)[getIndex(trace)] += 37;
 
   Expect.listEquals([-1, -2, -3, 42, 100, -4, 101, 37, -5, 42, 102], trace);
 }