Prevent redundant DoWorks due to canceled delayed tasks

third_party/WebKit/Source/platform/scheduler/base/time_domain.h

Index: third_party/WebKit/Source/platform/scheduler/base/time_domain.h
diff --git a/third_party/WebKit/Source/platform/scheduler/base/time_domain.h b/third_party/WebKit/Source/platform/scheduler/base/time_domain.h
index a9659b3aec17d700fa7f99b6e27272f221aabfe0..360ec49950021659203e9d00fb4db875281d92d4 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/time_domain.h
+++ b/third_party/WebKit/Source/platform/scheduler/base/time_domain.h
@@ -24,13 +24,17 @@ class TaskQueueImpl;
 class TaskQueueManager;
 class TaskQueueManagerDelegate;
 
-// The TimeDomain's job is to keep track of moments when delayed tasks have been
-// scheduled to fire and to notify their TaskQueues via UpdateDelayedWorkQueue.
+// The TimeDomain's job is to wake task queues up when their next delayed tasks
+// are due to fire. TaskQueues request a wake up via ScheduleDelayedWork, when
+// the WakeUp is due the TimeDomain calls TaskQueue::WakeUpForDelayedWork which
+// schedules the next non-canceled wakeup.
 //
-// The time domain keeps track of the next wakeup required to pump delayed tasks
-// and issues |RequestWakeup| calls to the subclass as needed.  Where possible
-// it tried to de-dupe these wakeups. Ideally it would be possible to cancel
-// them, but that's not currently supported by the base message loop.
+// To prevent spurious wake-ups for canceled tasks the TaskQueue should only
+// have a single wake up registered with its TimeDomain.  If should call
+// CancelDelayedWork as needed to ensure this. The TimeDomain communicates with
+// the TaskQueueManager to actually schedule the wake-ups on the underlying
+// base::MessageLoop. Various levels of de-duping are employed to prevent
+// unnecessary posting of TaskQueueManager::DoWork.
 //
 // The clock itself is provided by subclasses of the TimeDomain and it may be
 // the real wall clock or a synthetic (virtual) time base.
@@ -89,13 +93,13 @@ class BLINK_PLATFORM_EXPORT TimeDomain {
   // UpdateWorkQueue on.
   void RegisterAsUpdatableTaskQueue(internal::TaskQueueImpl* queue);
 
-  // Schedules a call to TaskQueueImpl::MoveReadyDelayedTasksToDelayedWorkQueue
+  // Schedules a call to TaskQueueImpl::WakeUpForDelayedWork
   // when this TimeDomain reaches |delayed_run_time|.
   void ScheduleDelayedWork(internal::TaskQueueImpl* queue,
                            base::TimeTicks delayed_run_time,
                            base::TimeTicks now);
 
-  // Cancels a call to TaskQueueImpl::MoveReadyDelayedTasksToDelayedWorkQueue
+  // Cancels a call to TaskQueueImpl::WakeUpForDelayedWork
   // previously requested with ScheduleDelayedWork.  Note this only works if
   // delayed_run_time is _not_ the next scheduled run time.
   void CancelDelayedWork(internal::TaskQueueImpl* queue,