Flush the SimpleBackendImpl's SWP in tests.

net/disk_cache/simple/simple_backend_impl.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/disk_cache/simple/simple_backend_impl.h"
 
 #include <algorithm>
 #include <cstdlib>
 
 #if defined(OS_POSIX)
@@ skipping 549 matching lines @@
     Entry** entry,
     const CompletionCallback& callback,
     int error_code) {
   if (error_code == net::ERR_FAILED) {
     OpenNextEntry(iter, entry, callback);
     return;
   }
   CallCompletionCallback(callback, error_code);
 }
 
+void SimpleBackendImpl::FlushWorkerPoolForTesting() {
+  if (g_sequenced_worker_pool)
+    g_sequenced_worker_pool->FlushForTesting();
+}
+
 }  // namespace disk_cache