Replace forward declarations with includes in TaskRunner APIs.

base/threading/thread_task_runner_handle.cc

 // Copyright 2016 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.
 
 #include "base/threading/thread_task_runner_handle.h"
 
 #include <utility>
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
-#include "base/single_thread_task_runner.h"
 #include "base/threading/sequenced_task_runner_handle.h"
 #include "base/threading/thread_local.h"
 
 namespace base {
 
 namespace {
 
 base::LazyInstance<base::ThreadLocalPointer<ThreadTaskRunnerHandle>>::Leaky
     lazy_tls_ptr = LAZY_INSTANCE_INITIALIZER;
 
@@ skipping 21 matching lines @@
   lazy_tls_ptr.Pointer()->Set(this);
 }
 
 ThreadTaskRunnerHandle::~ThreadTaskRunnerHandle() {
   DCHECK(task_runner_->BelongsToCurrentThread());
   DCHECK_EQ(lazy_tls_ptr.Pointer()->Get(), this);
   lazy_tls_ptr.Pointer()->Set(nullptr);
 }
 
 }  // namespace base