base: Re-apply WeakPtr support for SequencedWorkerPools, fixing deadlock

base/threading/sequenced_worker_pool.cc

 // 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.
 
 #include "base/threading/sequenced_worker_pool.h"
 
 #include <list>
 #include <map>
 #include <set>
 #include <utility>
@@ skipping 1106 matching lines @@
 }
 
 base::StaticAtomicSequenceNumber
 SequencedWorkerPool::Inner::g_last_sequence_number_;
 
 // SequencedWorkerPool --------------------------------------------------------
 
 // static
 SequencedWorkerPool::SequenceToken
 SequencedWorkerPool::GetSequenceTokenForCurrentThread() {
+  // Don't construct lazy instance on check.
+  if (g_lazy_tls_ptr == NULL)
+    return SequenceToken();
+
   SequencedWorkerPool::SequenceToken* token = g_lazy_tls_ptr.Get().Get();
   if (!token)
     return SequenceToken();
   return *token;
 }
 
 SequencedWorkerPool::SequencedWorkerPool(
     size_t max_threads,
     const std::string& thread_name_prefix)
     : constructor_message_loop_(MessageLoopProxy::current()),
@@ skipping 137 matching lines @@
 void SequencedWorkerPool::Shutdown(int max_new_blocking_tasks_after_shutdown) {
   DCHECK(constructor_message_loop_->BelongsToCurrentThread());
   inner_->Shutdown(max_new_blocking_tasks_after_shutdown);
 }
 
 bool SequencedWorkerPool::IsShutdownInProgress() {
   return inner_->IsShutdownInProgress();
 }
 
 }  // namespace base