Add comment against usage of base::Thread.

base/threading/thread.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_THREAD_H_
 #define BASE_THREADING_THREAD_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 10 matching lines @@
 #include "base/synchronization/lock.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/platform_thread.h"
 #include "build/build_config.h"
 
 namespace base {
 
 class MessagePump;
 class RunLoop;
 
+// IMPORTANT: Instead of creating a base::Thread, consider using
+// base::Create(Sequenced|SingleTreaded)TaskRunnerWithTraits().
+//
 // A simple thread abstraction that establishes a MessageLoop on a new thread.
 // The consumer uses the MessageLoop of the thread to cause code to execute on
 // the thread.  When this object is destroyed the thread is terminated.  All
 // pending tasks queued on the thread's message loop will run to completion
 // before the thread is terminated.
 //
 // WARNING! SUBCLASSES MUST CALL Stop() IN THEIR DESTRUCTORS!  See ~Thread().
 //
 // After the thread is stopped, the destruction sequence is:
 //
@@ skipping 291 matching lines @@
   // This class is not thread-safe, use this to verify access from the owning
   // sequence of the Thread.
   SequenceChecker owning_sequence_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_H_