Mark SequencedWorkerPool::GetWorkerPoolForCurrentThread() as deprecated.

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>
@@ skipping 148 matching lines @@
     virtual void OnDestruct() = 0;
   };
 
   // Gets the SequencedToken of the current thread.
   // If current thread is not a SequencedWorkerPool worker thread or is running
   // an unsequenced task, returns an invalid SequenceToken.
   static SequenceToken GetSequenceTokenForCurrentThread();
 
   // Returns the SequencedWorkerPool that owns this thread, or null if the
   // current thread is not a SequencedWorkerPool worker thread.
+  //
+  // Always returns nullptr when SequencedWorkerPool is redirected to
+  // TaskScheduler.
+  //
+  // DEPRECATED. Use SequencedTaskRunnerHandle::Get() instead. Consequentially
+  // the only remaining use case is in sequenced_task_runner_handle.cc to
+  // implement that and will soon be removed along with SequencedWorkerPool:
+  // http://crbug.com/622400.
   static scoped_refptr<SequencedWorkerPool> GetWorkerPoolForCurrentThread();
 
   // Returns a unique token that can be used to sequence tasks posted to
   // PostSequencedWorkerTask(). Valid tokens are always nonzero.
   static SequenceToken GetSequenceToken();
 
   // Starts redirecting tasks posted to this process' SequencedWorkerPools to
   // the registered TaskScheduler. This cannot be called after a task has been
   // posted to a SequencedWorkerPool. This is not thread-safe; proper
   // synchronization is required to use any SequencedWorkerPool method after
@@ skipping 216 matching lines @@
   // 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_