Remove unused include in sequenced_worker_pool.h

base/threading/sequenced_worker_pool.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_THREADING_SEQUENCED_WORKER_POOL_H_
 #define BASE_THREADING_SEQUENCED_WORKER_POOL_H_
 
 #include <stddef.h>
 
 #include <cstddef>
 #include <memory>
 #include <string>
 
 #include "base/base_export.h"
 #include "base/callback_forward.h"
+#include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "base/single_thread_task_runner.h"
 #include "base/task_runner.h"
 #include "base/task_scheduler/task_traits.h"
 
 namespace tracked_objects {
 class Location;
 }  // namespace tracked_objects
 
 namespace base {
 
-class SingleThreadTaskRunner;
+class SequencedTaskRunner;
 
 template <class T> class DeleteHelper;
 
-class SequencedTaskRunner;
-
 // A worker thread pool that enforces ordering between sets of tasks. It also
 // allows you to specify what should happen to your tasks on shutdown.
 //
 // To enforce ordering, get a unique sequence token from the pool and post all
 // tasks you want to order with the token. All tasks with the same token are
 // guaranteed to execute serially, though not necessarily on the same thread.
 // This means that:
 //
 //   - No two tasks with the same token will run at the same time.
 //
@@ skipping 181 matching lines @@
   // function multiple times with the same string will always produce the
   // same sequence token. If the name has not been used before, a new token
   // will be created.
   SequenceToken GetNamedSequenceToken(const std::string& name);
 
   // Returns a SequencedTaskRunner wrapper which posts to this
   // SequencedWorkerPool using the given sequence token. Tasks with nonzero
   // delay are posted with SKIP_ON_SHUTDOWN behavior and tasks with zero delay
   // are posted with BLOCK_SHUTDOWN behavior.
   scoped_refptr<SequencedTaskRunner> GetSequencedTaskRunner(
-      SequenceToken token);
+      SequenceToken token) WARN_UNUSED_RESULT;

[gab, 2016/10/28 20:30:11]

By the IWUU described in description this would have required #include
"sequenced_task_runner.h" which defeats the purpose of what I'm trying to
achieve in this CL (break a dependency cycle involving sequenced_task_runner.h).

The reason IWUU dictates that a return by value must be fully defined by the API
providing it is so that the caller doesn't need include things for return values
it ignores. In this case it doesn't make sense to ignore these return values and
as such I think this is okay.

[danakj, 2016/10/29 00:01:28]

It's going to maybe bite us if we ever get auto iwyu, but then what isn't?

 
   // Returns a SequencedTaskRunner wrapper which posts to this
   // SequencedWorkerPool using the given sequence token. Tasks with nonzero
   // delay are posted with SKIP_ON_SHUTDOWN behavior and tasks with zero delay
   // are posted with the given shutdown behavior.
   scoped_refptr<SequencedTaskRunner> GetSequencedTaskRunnerWithShutdownBehavior(
       SequenceToken token,
-      WorkerShutdown shutdown_behavior);
+      WorkerShutdown shutdown_behavior) WARN_UNUSED_RESULT;
 
   // Returns a TaskRunner wrapper which posts to this SequencedWorkerPool using
   // the given shutdown behavior. Tasks with nonzero delay are posted with
   // SKIP_ON_SHUTDOWN behavior and tasks with zero delay are posted with the
   // given shutdown behavior.
   scoped_refptr<TaskRunner> GetTaskRunnerWithShutdownBehavior(
-      WorkerShutdown shutdown_behavior);
+      WorkerShutdown shutdown_behavior) WARN_UNUSED_RESULT;
 
   // Posts the given task for execution in the worker pool. Tasks posted with
   // this function will execute in an unspecified order on a background thread.
   // Returns true if the task was posted. If your tasks have ordering
   // requirements, see PostSequencedWorkerTask().
   //
   // This class will attempt to delete tasks that aren't run
   // (non-block-shutdown semantics) but can't guarantee that this happens. If
   // all worker threads are busy running CONTINUE_ON_SHUTDOWN tasks, there
   // will be no workers available to delete these tasks. And there may be
@@ skipping 130 matching lines @@
   friend class DeleteHelper<SequencedWorkerPool>;
 
   class Inner;
   class PoolSequencedTaskRunner;
   class Worker;
 
   // Returns true if the current thread is processing a task with the given
   // sequence_token.
   bool IsRunningSequenceOnCurrentThread(SequenceToken sequence_token) const;
 
-  const scoped_refptr<SingleThreadTaskRunner> constructor_task_runner_;
+  const scoped_refptr<SequencedTaskRunner> constructor_task_runner_;
 
   // Avoid pulling in too many headers by putting (almost) everything
   // into |inner_|.
   const std::unique_ptr<Inner> inner_;
 
   DISALLOW_COPY_AND_ASSIGN(SequencedWorkerPool);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_SEQUENCED_WORKER_POOL_H_