Remove base::mac::LibDispatchTaskRunner and migrate its sole client to plain libdispatch.

base/mac/libdispatch_task_runner.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_MAC_LIBDISPATCH_TASK_RUNNER_H_
-#define BASE_MAC_LIBDISPATCH_TASK_RUNNER_H_
-
-#include <dispatch/dispatch.h>
-
-#include "base/single_thread_task_runner.h"
-#include "base/synchronization/waitable_event.h"
-
-namespace base {
-namespace mac {
-
-// This is an implementation of the TaskRunner interface that runs closures on
-// a thread managed by Apple's libdispatch. This has the benefit of being able
-// to PostTask() and friends to a dispatch queue, while being reusable as a
-// dispatch_queue_t.
-//
-// One would use this class if an object lives exclusively on one thread but
-// needs a dispatch_queue_t for use in a system API. This ensures all dispatch
-// callbacks happen on the same thread as Closure tasks.
-//
-// A LibDispatchTaskRunner will continue to run until all references to the
-// underlying dispatch queue are released.
-//
-// Important Notes:
-//   - There is no MessageLoop running on this thread, and ::current() returns
-//     NULL.
-//   - No nested loops can be run, and all tasks are run non-nested.
-//   - Work scheduled via libdispatch runs at the same priority as and is
-//     interleaved with posted tasks, though FIFO order is guaranteed.
-//
-class BASE_EXPORT LibDispatchTaskRunner : public base::SingleThreadTaskRunner {
- public:
-  // Starts a new serial dispatch queue with a given name.
-  explicit LibDispatchTaskRunner(const char* name);
-
-  // base::TaskRunner:
-  bool PostDelayedTask(const tracked_objects::Location& from_here,
-                       const Closure& task,
-                       base::TimeDelta delay) override;
-  bool RunsTasksOnCurrentThread() const override;
-
-  // base::SequencedTaskRunner:
-  bool PostNonNestableDelayedTask(const tracked_objects::Location& from_here,
-                                  const Closure& task,
-                                  base::TimeDelta delay) override;
-
-  // This blocks the calling thread until all work on the dispatch queue has
-  // been run and the queue has been destroyed. Destroying a queue requires
-  // ALL retained references to it to be released. Any new tasks posted to
-  // this thread after shutdown are dropped.
-  void Shutdown();
-
-  // Returns the dispatch queue associated with this task runner, for use with
-  // system APIs that take dispatch queues. The caller is responsible for
-  // retaining the result.
-  //
-  // All properties (context, finalizer, etc.) are managed by this class, and
-  // clients should only use the result of this for dispatch_async().
-  dispatch_queue_t GetDispatchQueue() const;
-
- protected:
-  ~LibDispatchTaskRunner() override;
-
- private:
-  static void Finalizer(void* context);
-
-  dispatch_queue_t queue_;
-
-  // The event on which Shutdown waits until Finalizer runs.
-  base::WaitableEvent queue_finalized_;
-};
-
-}  // namespace mac
-}  // namespace base
-
-#endif  // BASE_MAC_LIBDISPATCH_TASK_RUNNER_H_