Remove base::WorkerPool.

This class is deprecated and no longer used.

TBR=agl@chromium.org,holte@chromium.org

Bug: 659191, 251774
Change-Id: I111c334d3feac302abd14aa9d4d142aa237a00b4
Reviewed-on: https://chromium-review.googlesource.com/650368
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504708}

base/BUILD.gn

@@ -896,11 +896,6 @@ component("base") {
     "threading/thread_task_runner_handle.h",
     "threading/watchdog.cc",
     "threading/watchdog.h",
-    "threading/worker_pool.cc",
-    "threading/worker_pool.h",
-    "threading/worker_pool_posix.cc",
-    "threading/worker_pool_posix.h",
-    "threading/worker_pool_win.cc",
     "time/clock.cc",
     "time/clock.h",
     "time/default_clock.cc",
@@ -2195,8 +2190,6 @@ test("base_unittests") {
     "threading/thread_task_runner_handle_unittest.cc",
     "threading/thread_unittest.cc",
     "threading/watchdog_unittest.cc",
-    "threading/worker_pool_posix_unittest.cc",
-    "threading/worker_pool_unittest.cc",
     "time/pr_time_unittest.cc",
     "time/time_unittest.cc",
     "time/time_win_unittest.cc",

base/threading/post_task_and_reply_impl.h

@@ -2,8 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// This file contains the implementation shared by
-// TaskRunner::PostTaskAndReply and WorkerPool::PostTaskAndReply.
+// This file contains the implementation for TaskRunner::PostTaskAndReply.
 
 #ifndef BASE_THREADING_POST_TASK_AND_REPLY_IMPL_H_
 #define BASE_THREADING_POST_TASK_AND_REPLY_IMPL_H_
@@ -19,7 +18,9 @@ namespace internal {
 // custom execution context.
 //
 // If you're looking for a concrete implementation of PostTaskAndReply, you
-// probably want base::TaskRunner, or you may want base::WorkerPool.
+// probably want base::TaskRunner.
+//
+// TODO(fdoray): Move this to the anonymous namespace of base/task_runner.cc.
 class BASE_EXPORT PostTaskAndReplyImpl {
  public:
   virtual ~PostTaskAndReplyImpl() = default;

base/threading/sequenced_worker_pool.h

@@ -65,11 +65,6 @@ template <class T> class DeleteHelper;
 // for CONTINUE_ON_SHUTDOWN behavior and is required for BLOCK_SHUTDOWN
 // behavior.
 //
-// Implementation note: This does not use a base::WorkerPool since that does
-// not enforce shutdown semantics or allow us to specify how many worker
-// threads to run. For the typical use case of random background work, we don't
-// necessarily want to be super aggressive about creating threads.
-//
 // Note that SequencedWorkerPool is RefCountedThreadSafe (inherited
 // from TaskRunner).
 //