Hook up the SequencedWorkerPool to the browser thread.

base/threading/sequenced_worker_pool.h

 // Copyright (c) 2011 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_SEQUENCED_WORKER_POOL_H_
 #define BASE_THREADING_SEQUENCED_WORKER_POOL_H_
 #pragma once
 
 #include <string>
 
@@ skipping 75 matching lines @@
     BLOCK_SHUTDOWN,
   };
 
   // Opaque identifier that defines sequencing of tasks posted to the worker
   // pool. See NewSequenceToken().
   class SequenceToken {
    public:
     explicit SequenceToken() : id_(0) {}
     ~SequenceToken() {}
 
+    // Returns true if this is a null sequence token. The null sequence token
+    // has not been initialized.
+    bool is_null() const { return id_ == 0; }
+
     bool Equals(const SequenceToken& other) const {
       return id_ == other.id_;
     }
 
    private:
     friend class SequencedWorkerPool;
 
     SequenceToken(int id) : id_(id) {}
 
     int id_;
@@ skipping 91 matching lines @@
   friend class Worker;
 
   scoped_refptr<Inner> inner_;
 
   DISALLOW_COPY_AND_ASSIGN(SequencedWorkerPool);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_SEQUENCED_WORKER_POOL_H_