Do not block in SimpleThread::Start().

content/renderer/categorized_worker_pool.h

 // 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.
 
 #ifndef CONTENT_RENDERER_CATEGORIZED_WORKER_POOL_H_
 #define CONTENT_RENDERER_CATEGORIZED_WORKER_POOL_H_
 
 #include <memory>
 
 #include "base/callback.h"
@@ skipping 51 matching lines @@
   // of all the associated task runners.
   // Once all the tasks are executed the method blocks until the threads are
   // terminated.
   void Shutdown();
 
   cc::TaskGraphRunner* GetTaskGraphRunner() { return this; }
 
   // Create a new sequenced task graph runner.
   scoped_refptr<base::SequencedTaskRunner> CreateSequencedTaskRunner();
 
-  base::PlatformThreadId background_worker_thread_id() const {
-    return threads_.back()->tid();
-  }
+  // Blocks until the background worker is running.
+  base::PlatformThreadId GetBackgroundWorkerThreadId() const;
 
  protected:
   ~CategorizedWorkerPool() override;
 
  private:
   class CategorizedWorkerPoolSequencedTaskRunner;
   friend class CategorizedWorkerPoolSequencedTaskRunner;
 
   // Simple Task for the TaskGraphRunner that wraps a closure.
   // This class is used to schedule TaskRunner tasks on the
@@ skipping 58 matching lines @@
   // Condition variable that is waited on by origin threads until a namespace
   // has finished running all associated tasks.
   base::ConditionVariable has_namespaces_with_finished_running_tasks_cv_;
   // Set during shutdown. Tells Run() to return when no more tasks are pending.
   bool shutdown_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_CATEGORIZED_WORKER_POOL_H_