Reland of Tests: Simplify SequencedWorkerPoolOwner, call Shutdown on destructor.

base/test/sequenced_worker_pool_owner.h

 // Copyright (c) 2012 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.
 
 #ifndef BASE_TEST_SEQUENCED_WORKER_POOL_OWNER_H_
 #define BASE_TEST_SEQUENCED_WORKER_POOL_OWNER_H_
 
 #include <cstddef>
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
+#include "base/run_loop.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/sequenced_worker_pool.h"
 
 namespace base {
 
 class MessageLoop;
 
 // Wrapper around SequencedWorkerPool for testing that blocks destruction
 // until the pool is actually destroyed.  This is so that a
 // SequencedWorkerPool from one test doesn't outlive its test and cause
 // strange races with other tests that touch global stuff (like histograms and
 // logging).  However, this requires that nothing else on this thread holds a
 // ref to the pool when the SequencedWorkerPoolOwner is destroyed.
+//
+// This class calls Shutdown on the owned SequencedWorkerPool in the destructor.
+// Tests may themselves call Shutdown earlier to test shutdown behavior.
 class SequencedWorkerPoolOwner : public SequencedWorkerPool::TestingObserver {
  public:
   SequencedWorkerPoolOwner(size_t max_threads,
                            const std::string& thread_name_prefix);
 
   ~SequencedWorkerPoolOwner() override;
 
   // Don't change the returned pool's testing observer.
   const scoped_refptr<SequencedWorkerPool>& pool();
 
   // The given callback will be called on WillWaitForShutdown().
   void SetWillWaitForShutdownCallback(const Closure& callback);
 
   int has_work_call_count() const;
 
  private:
   // SequencedWorkerPool::TestingObserver implementation.
   void OnHasWork() override;
   void WillWaitForShutdown() override;
   void OnDestruct() override;
 
+  // Used to run the current thread's message loop until the
+  // SequencedWorkerPool's destruction has been verified.
+  base::RunLoop exit_loop_;
   MessageLoop* const constructor_message_loop_;
+
   scoped_refptr<SequencedWorkerPool> pool_;
   Closure will_wait_for_shutdown_callback_;
 
   mutable Lock has_work_lock_;
   int has_work_call_count_;
 
   DISALLOW_COPY_AND_ASSIGN(SequencedWorkerPoolOwner);
 };
 
 }  // namespace base
 
 #endif  // BASE_TEST_SEQUENCED_WORKER_POOL_OWNER_H_