Revert of Do not block in SimpleThread::Start().

content/renderer/categorized_worker_pool.cc

 // Copyright 2015 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 "content/renderer/categorized_worker_pool.h"
 
 #include <string>
 #include <utility>
 #include <vector>
 
@@ skipping 238 matching lines @@
   while (!work_queue_.HasFinishedRunningTasksInAllNamespaces()) {
     has_namespaces_with_finished_running_tasks_cv_.Wait();
   }
 }
 
 scoped_refptr<base::SequencedTaskRunner>
 CategorizedWorkerPool::CreateSequencedTaskRunner() {
   return new CategorizedWorkerPoolSequencedTaskRunner(this);
 }
 
-base::PlatformThreadId CategorizedWorkerPool::GetBackgroundWorkerThreadId()
-    const {
-  return threads_.back()->GetTid();
-}
-
 CategorizedWorkerPool::~CategorizedWorkerPool() {}
 
 cc::NamespaceToken CategorizedWorkerPool::GenerateNamespaceToken() {
   base::AutoLock lock(lock_);
   return work_queue_.GenerateNamespaceToken();
 }
 
 void CategorizedWorkerPool::ScheduleTasks(cc::NamespaceToken token,
                                           cc::TaskGraph* graph) {
   TRACE_EVENT2("disabled-by-default-cc.debug",
@@ skipping 150 matching lines @@
 
 // Overridden from cc::Task:
 void CategorizedWorkerPool::ClosureTask::RunOnWorkerThread() {
   closure_.Run();
   closure_.Reset();
 }
 
 CategorizedWorkerPool::ClosureTask::~ClosureTask() {}
 
 }  // namespace content