Fix a test launcher hang when no tests are run.

base/test/parallel_test_launcher.cc

 // Copyright 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 "base/test/parallel_test_launcher.h"
 
 #if defined(OS_POSIX)
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ skipping 116 matching lines @@
              this,
              &ParallelTestLauncher::OnOutputTimeout),
       launch_sequence_number_(0),
       worker_pool_(new SequencedWorkerPool(jobs, "parallel_test_launcher")) {
   // Start the watchdog timer.
   timer_.Reset();
 }
 
 ParallelTestLauncher::~ParallelTestLauncher() {
   DCHECK(thread_checker_.CalledOnValidThread());
+
+  worker_pool_->Shutdown();
 }
 
 void ParallelTestLauncher::LaunchChildGTestProcess(
     const CommandLine& command_line,
     const std::string& wrapper,
     base::TimeDelta timeout,
     const LaunchChildGTestProcessCallback& callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
   // Record the exact command line used to launch the child.
@@ skipping 46 matching lines @@
 #endif
   }
 
   fflush(stdout);
 
   // Arm the timer again - otherwise it would fire only once.
   timer_.Reset();
 }
 
 }  // namespace base