Moves code collection test to io

tests/standalone/io/code_collection_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.
 
 // Dart test program testing code GC.
 
 import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 
@@ skipping 48 matching lines @@
     // message that foo's code was dropped.
     var found = false;
     pr.stdout.split("\n").forEach((line) {
       if (line.contains("Detaching code") && line.contains("foo")) {
         found = true;
       }
     });
     Expect.isTrue(found);
   }
 }