Remove unused include in sequenced_worker_pool.h

base/threading/sequenced_worker_pool.h

Index: base/threading/sequenced_worker_pool.h
diff --git a/base/threading/sequenced_worker_pool.h b/base/threading/sequenced_worker_pool.h
index f06a9e523cc530047de4d55b91f0eb745efc8566..252d511d3f2bae0f09738c0939d0d2932dc10877 100644
--- a/base/threading/sequenced_worker_pool.h
+++ b/base/threading/sequenced_worker_pool.h
@@ -13,9 +13,9 @@
 
 #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"
 
@@ -25,12 +25,10 @@ class Location;
 
 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.
 //
@@ -232,7 +230,7 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
   // 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
@@ -240,14 +238,14 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
   // 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.
@@ -398,7 +396,7 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
   // 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_|.