[Reland] Make canceling Timers fast.

third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc

 // Copyright 2014 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 "platform/scheduler/base/task_queue_manager.h"
 
 #include <queue>
 #include <set>
 
 #include "base/bind.h"
@@ skipping 259 matching lines @@
     const internal::TaskQueueImpl::Task& pending_task) {
   task_annotator_.DidQueueTask("TaskQueueManager::PostTask", pending_task);
 }
 
 TaskQueueManager::ProcessTaskResult TaskQueueManager::ProcessTaskFromWorkQueue(
     internal::WorkQueue* work_queue) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   scoped_refptr<DeletionSentinel> protect(deletion_sentinel_);
   internal::TaskQueueImpl* queue = work_queue->task_queue();
 
   if (queue->GetQuiescenceMonitored())

[Sami, 2016/09/08 16:35:02]

Might want to move this below the early-out.

[alex clarke (OOO till 29th), 2016/09/08 16:43:28]

Done.

     task_was_run_on_quiescence_monitored_queue_ = true;
 
   internal::TaskQueueImpl::Task pending_task =
       work_queue->TakeTaskFromWorkQueue();
+
+  // It's possible the task was canceled, if so bail out.
+  if (pending_task.task.IsCancelled())
+    return ProcessTaskResult::EXECUTED;
+
   if (!pending_task.nestable && delegate_->IsNested()) {
     // Defer non-nestable work to the main task runner.  NOTE these tasks can be
     // arbitrarily delayed so the additional delay should not be a problem.
     // TODO(skyostil): Figure out a way to not forget which task queue the
     // task is associated with. See http://crbug.com/522843.
-    delegate_->PostNonNestableTask(pending_task.posted_from, pending_task.task);
+    delegate_->PostNonNestableTask(pending_task.posted_from,
+                                   std::move(pending_task.task));
     return ProcessTaskResult::DEFERRED;
   }
 
   MaybeRecordTaskDelayHistograms(pending_task, queue);
 
   TRACE_TASK_EXECUTION("TaskQueueManager::ProcessTaskFromWorkQueue",
                        pending_task);
   if (queue->GetShouldNotifyObservers()) {
     FOR_EACH_OBSERVER(base::MessageLoop::TaskObserver, task_observers_,
                       WillProcessTask(pending_task));
@@ skipping 131 matching lines @@
   DCHECK(main_thread_checker_.CalledOnValidThread());
   DCHECK(!work_queue->Empty());
   if (observer_) {
     observer_->OnTriedToExecuteBlockedTask(*work_queue->task_queue(),
                                            *work_queue->GetFrontTask());
   }
 }
 
 }  // namespace scheduler
 }  // namespace blink