base: Change WeakPtr to use SequenceChecker instead of ThreadChecker.

base/sequence_checker_impl.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/sequence_checker_impl.h"
 
-#include "base/sequenced_task_runner.h"
+#include "base/logging.h"
 
 namespace base {
 
-SequenceCheckerImpl::SequenceCheckerImpl(
-    const scoped_refptr<SequencedTaskRunner>& sequenced_task_runner)
-    : sequenced_task_runner_(sequenced_task_runner) {}
+SequenceCheckerImpl::SequenceCheckerImpl()
+    : sequence_token_assigned_(false),
+      has_sequence_(false) {
+  EnsureSequenceTokenAssigned();
+}
 
 SequenceCheckerImpl::~SequenceCheckerImpl() {}
 
 bool SequenceCheckerImpl::CalledOnValidSequence() const {
+  EnsureSequenceTokenAssigned();
   AutoLock auto_lock(lock_);
-  return sequenced_task_runner_.get() ?
-      sequenced_task_runner_->RunsTasksOnCurrentThread() :
-      thread_checker_.CalledOnValidThread();
+
+  // If this thread is not associated with a SequencedWorkerPool,
+  // SequenceChecker behaves as a ThreadChecker. See header for details.
+  if (!has_sequence_)
+    return thread_checker_.CalledOnValidThread();
+
+  SequencedWorkerPool::SequenceToken current_token;
+  if (!SequencedWorkerPool::CurrentThreadSequenceToken(&current_token))
+    return false;
+
+  return sequence_token_.Equals(current_token);
 }
 
-void SequenceCheckerImpl::ChangeSequence(
-    const scoped_refptr<SequencedTaskRunner>& sequenced_task_runner) {
+void SequenceCheckerImpl::DetachFromSequence() {
   AutoLock auto_lock(lock_);
-  sequenced_task_runner_ = sequenced_task_runner;
   thread_checker_.DetachFromThread();
+  sequence_token_assigned_ = false;
+  has_sequence_ = false;
+  sequence_token_ = SequencedWorkerPool::SequenceToken();
+}
+
+void SequenceCheckerImpl::EnsureSequenceTokenAssigned() const {
+  AutoLock auto_lock(lock_);
+  if (sequence_token_assigned_)
+    return;
+
+  sequence_token_assigned_ = true;
+  has_sequence_ =
+      SequencedWorkerPool::CurrentThreadSequenceToken(&sequence_token_);
 }
 
 }  // namespace base