Revert 211956 "base: Change WeakPtr to use SequenceChecker inste..."

base/sequence_checker_impl.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_SEQUENCE_CHECKER_IMPL_H_
 #define BASE_SEQUENCE_CHECKER_IMPL_H_
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
-#include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/thread_checker_impl.h"
 
 namespace base {
 
+class SequencedTaskRunner;
+
 // SequenceCheckerImpl is used to help verify that some methods of a
 // class are called in sequence -- that is, called from the same
 // SequencedTaskRunner. It is a generalization of ThreadChecker; in
-// particular, it behaves exactly like ThreadChecker if constructed
-// on a thread that is not part of a SequencedWorkerPool.
+// particular, it behaves exactly like ThreadChecker if its passed a
+// NULL SequencedTaskRunner.
 class BASE_EXPORT SequenceCheckerImpl {
  public:
-  SequenceCheckerImpl();
+  // |sequenced_task_runner| can be NULL.  In that case, this object
+  // behaves exactly like a ThreadChecker bound to the current thread,
+  // i.e.  CalledOnValidSequence() behaves like CalledOnValidThread().
+  explicit SequenceCheckerImpl(
+      const scoped_refptr<SequencedTaskRunner>& sequenced_task_runner);
   ~SequenceCheckerImpl();
 
-  // Returns whether the we are being called on the same sequence token
-  // as previous calls. If there is no associated sequence, then returns
-  // whether we are being called on the underlying ThreadChecker's thread.
-  bool CalledOnValidSequencedThread() const;
+  // Returns whether the we are being called on the underyling
+  // SequencedTaskRunner.  If we're not bound to a
+  // |sequenced_task_runner|, returns whether we are being called on
+  // the underlying ThreadChecker's thread.
+  bool CalledOnValidSequence() const;
 
-  // Unbinds the checker from the currently associated sequence. The
-  // checker will be re-bound on the next call to CalledOnValidSequence().
-  void DetachFromSequence();
+  // Changes the underyling SequencedTaskRunner.
+  // |sequenced_task_runner| can be NULL.  In that case, this object
+  // behaves exactly like a ThreadChecker that has been detached from
+  // its thread, i.e. we will be bound to the thread on which we next
+  // call CalledOnValidSequence().
+  void ChangeSequence(
+      const scoped_refptr<SequencedTaskRunner>& sequenced_task_runner);
 
  private:
-  void EnsureSequenceTokenAssigned() const;
-
   // Guards all variables below.
   mutable Lock lock_;
-
-  // Used if |sequence_token_| is not valid.
+  scoped_refptr<SequencedTaskRunner> sequenced_task_runner_;
+  // Used if |sequenced_task_runner_| is NULL.
   ThreadCheckerImpl thread_checker_;
-  mutable bool sequence_token_assigned_;
-
-  mutable SequencedWorkerPool::SequenceToken sequence_token_;
 
   DISALLOW_COPY_AND_ASSIGN(SequenceCheckerImpl);
 };
 
 }  // namespace base
 
 #endif  // BASE_SEQUENCE_CHECKER_IMPL_H_