Fix incorrect memory barrier usage I previously asked to be introduced.

base/message_loop/message_loop.cc

 // Copyright 2013 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/message_loop/message_loop.h"
 
 #include <algorithm>
 #include <memory>
 #include <utility>
 
@@ skipping 400 matching lines @@
   else
     pump_ = CreateMessagePumpForType(type_);
 
   DCHECK(!current()) << "should only have one message loop per thread";
   lazy_tls_ptr.Pointer()->Set(this);
 
   incoming_task_queue_->StartScheduling();
   unbound_task_runner_->BindToCurrentThread();
   unbound_task_runner_ = nullptr;
   SetThreadTaskRunnerHandle();
-  {
-    // Save the current thread's ID for potential use by other threads
-    // later from GetThreadName().
-    thread_id_ = PlatformThread::CurrentId();
-    subtle::MemoryBarrier();
-  }
+  thread_id_ = PlatformThread::CurrentId();
 }
 
 std::string MessageLoop::GetThreadName() const {
-  if (thread_id_ == kInvalidThreadId) {
-    // |thread_id_| may already have been initialized but this thread might not
-    // have received the update yet.
-    subtle::MemoryBarrier();
-    DCHECK_NE(kInvalidThreadId, thread_id_);
-  }
+  DCHECK_NE(kInvalidThreadId, thread_id_)
+      << "GetThreadName() must only be called after BindToCurrentThread()'s "
+      << "side-effects have been synchronized with this thread.";
   return ThreadIdNameManager::GetInstance()->GetName(thread_id_);
 }
 
 void MessageLoop::SetTaskRunner(
     scoped_refptr<SingleThreadTaskRunner> task_runner) {
   DCHECK_EQ(this, current());
   DCHECK(task_runner->BelongsToCurrentThread());
   DCHECK(!unbound_task_runner_);
   task_runner_ = std::move(task_runner);
   SetThreadTaskRunnerHandle();
@@ skipping 325 matching lines @@
       persistent,
       mode,
       controller,
       delegate);
 }
 #endif
 
 #endif  // !defined(OS_NACL_SFI)
 
 }  // namespace base