base: Change WeakPtr to use SequenceChecker instead of ThreadChecker.

base/threading/sequenced_worker_pool.h

Index: base/threading/sequenced_worker_pool.h
diff --git a/base/threading/sequenced_worker_pool.h b/base/threading/sequenced_worker_pool.h
index 7e04b071428c838dfcec0faa647f82baf2932045..aa585de3c3baa108135557623260060bbee58750 100644
--- a/base/threading/sequenced_worker_pool.h
+++ b/base/threading/sequenced_worker_pool.h
@@ -159,7 +159,7 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
                       TestingObserver* observer);
 
   // Returns a unique token that can be used to sequence tasks posted to
-  // PostSequencedWorkerTask(). Valid tokens are alwys nonzero.
+  // PostSequencedWorkerTask(). Valid tokens are always nonzero.
   SequenceToken GetSequenceToken();
 
   // Returns the sequence token associated with the given name. Calling this
@@ -168,6 +168,11 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
   // will be created.
   SequenceToken GetNamedSequenceToken(const std::string& name);
 
+  // Retrieves the sequence token associated with the current thread.
+  // If current thread is not part in worker pool, this returns false and
+  // |result_token| is unmodified. |result_token| may not be NULL.
+  bool GetCurrentThreadSequenceToken(SequenceToken* result_token) const;
+
   // Returns a SequencedTaskRunner wrapper which posts to this
   // SequencedWorkerPool using the given sequence token. Tasks with nonzero
   // delay are posted with SKIP_ON_SHUTDOWN behavior and tasks with zero delay
@@ -322,6 +327,11 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
   virtual void OnDestruct() const OVERRIDE;
 
  private:
+  friend class SequenceCheckerImpl;
+
+  // Gets the SequencedWorkerPool that owns the current thread. May be NULL.
+  static SequencedWorkerPool* Owner();
+
   friend class RefCountedThreadSafe<SequencedWorkerPool>;
   friend class DeleteHelper<SequencedWorkerPool>;