Move js perf test to another directory.

test/js-perf-test/Collections/weakset.js

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 var SetBenchmark = new BenchmarkSuite('WeakSet', [1000], [
   new Benchmark('Add', false, false, 0, WeakSetAdd),
   new Benchmark('Has', false, false, 0, WeakSetHas, WeakSetSetup,
       WeakSetTearDown),
   new Benchmark('Delete', false, false, 0, WeakSetDelete, WeakSetSetup,
@@ skipping 44 matching lines @@
 }
 
 
 function WeakSetDelete() {
   // This is run more than once per setup so we will end up deleting items
   // more than once. Therefore, we do not the return value of delete.
   for (var i = 0; i < N; i++) {
     ws.delete(keys[i]);
   }
 }