Remove dependency of SSLPlatformKeyTaskRunner on single-threaded SequencedWorkerPool.

net/ssl/ssl_platform_key_task_runner.h

 // Copyright 2015 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 NET_SSL_SSL_PLATFORM_KEY_TASK_RUNNER_H_
 #define NET_SSL_SSL_PLATFORM_KEY_TASK_RUNNER_H_
 
 #include "base/macros.h"
-#include "base/threading/sequenced_worker_pool.h"
+#include "base/memory/ref_counted.h"
+#include "base/threading/thread.h"
+
+namespace {
+class SingleThreadTaskRunner;

[Ryan Sleevi, 2016/07/27 19:09:23]

BUG: wrong namespace; should be base, but you've got this unnamed.

[gab, 2016/07/28 18:30:34]

Oops, good eyes, done.

+}

[Ryan Sleevi, 2016/07/27 19:09:23]

STYLE: }  // namespace base

[gab, 2016/07/28 18:30:34]

I've been told (by danakj@) that for small fwd-decl blocks (< ~6) we typically
omit the closing comment.

 
 namespace net {
 
-// Serialize all the private key operations on a single background
-// thread to avoid problems with buggy smartcards.
+// Serialize all the private key operations on a single background thread to
+// avoid problems with buggy smartcards. Its underlying Thread is non-joinable
+// and as such provides TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN semantics.
 class SSLPlatformKeyTaskRunner {
  public:
   SSLPlatformKeyTaskRunner();
   ~SSLPlatformKeyTaskRunner();
 
-  scoped_refptr<base::SequencedTaskRunner> task_runner();
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner();
 
  private:
-  scoped_refptr<base::SequencedWorkerPool> worker_pool_;
-  scoped_refptr<base::SequencedTaskRunner> task_runner_;
+  base::Thread worker_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(SSLPlatformKeyTaskRunner);
 };
 
-scoped_refptr<base::SequencedTaskRunner> GetSSLPlatformKeyTaskRunner();
+scoped_refptr<base::SingleThreadTaskRunner> GetSSLPlatformKeyTaskRunner();
 
 }  // namespace net
 
 #endif  // NET_SSL_SSL_PLATFORM_KEY_TASK_RUNNER_H_