[Try # 3] Scheduler refactoring to virtually eliminate redundant DoWorks

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 639d1742a35feec99c4355430a72a7ab048b076a..3d454077fa359aa9a6d0b815ec8c176c08c155f4 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/time_domain.h
+++ b/third_party/WebKit/Source/platform/scheduler/base/time_domain.h
@@ -62,9 +62,11 @@ class BLINK_PLATFORM_EXPORT TimeDomain {
   // Evaluate this TimeDomain's Now. Can be called from any thread.
   virtual base::TimeTicks Now() const = 0;
 
-  // Some TimeDomains support virtual time, this method tells us to advance time
-  // if possible and return true if time was advanced.
-  virtual bool MaybeAdvanceTime() = 0;
+  // Computes the delay until the next task the TimeDomain is aware of, if any.
+  // Note virtual time domains may return base::TimeDelta() if they have any
+  // tasks that are eligible to run.
+  virtual base::Optional<base::TimeDelta> DelayTillNextTask(
+      LazyNow* lazy_now) = 0;
 
   // Returns the name of this time domain for tracing.
   virtual const char* GetName() const = 0;
@@ -80,18 +82,14 @@ class BLINK_PLATFORM_EXPORT TimeDomain {
   void AsValueInto(base::trace_event::TracedValue* state) const;
 
   // Migrates |queue| from this time domain to |destination_time_domain|.
-  // Main-thread only.
-  void MigrateQueue(internal::TaskQueueImpl* queue,
-                    TimeDomain* destination_time_domain);
+  // Main-thread only.  Returns the time of the scheduled wakeup if any,
+  base::TimeTicks MigrateQueue(internal::TaskQueueImpl* queue,
+                               TimeDomain* destination_time_domain);
 
   // If there is a scheduled delayed task, |out_task_queue| is set to the queue
   // the next task was posted to and it returns true.  Returns false otherwise.
   bool NextScheduledTaskQueue(TaskQueue** out_task_queue) const;
 
-  // Adds |queue| to the set of task queues that UpdateWorkQueues calls
-  // UpdateWorkQueue on.
-  void RegisterAsUpdatableTaskQueue(internal::TaskQueueImpl* queue);
-
   // Schedules a call to TaskQueueImpl::WakeUpForDelayedWork when this
   // TimeDomain reaches |delayed_run_time|.  This supersedes any previously
   // registered wakeup for |queue|.
@@ -99,18 +97,19 @@ class BLINK_PLATFORM_EXPORT TimeDomain {
                            base::TimeTicks delayed_run_time,
                            base::TimeTicks now);
 
+  // Cancels any scheduled calls to TaskQueueImpl::WakeUpForDelayedWork for
+  // |queue|.
+  void CancelDelayedWork(internal::TaskQueueImpl* queue);
+
   // Registers the |queue|.
   void RegisterQueue(internal::TaskQueueImpl* queue);
 
-  // Removes |queue| from the set of task queues that UpdateWorkQueues calls
-  // UpdateWorkQueue on. Returns true if |queue| was updatable.
-  bool UnregisterAsUpdatableTaskQueue(internal::TaskQueueImpl* queue);
-
   // Removes |queue| from all internal data structures.
   void UnregisterQueue(internal::TaskQueueImpl* queue);
 
-  // Updates active queues associated with this TimeDomain.
-  void UpdateWorkQueues(LazyNow lazy_now);
+  // Tells the time domain that |queue| went from having no immediate work to
+  // having some.
+  void OnQueueHasImmediateWork(internal::TaskQueueImpl* queue);
 
   // Called by the TaskQueueManager when the TimeDomain is registered.
   virtual void OnRegisterWithTaskQueueManager(
@@ -136,8 +135,6 @@ class BLINK_PLATFORM_EXPORT TimeDomain {
   }
 
  private:
-  void MoveNewlyUpdatableQueuesIntoUpdatableQueueSet();
-
   struct DelayedWakeup {
     base::TimeTicks time;
     internal::TaskQueueImpl* queue;
@@ -164,16 +161,7 @@ class BLINK_PLATFORM_EXPORT TimeDomain {
 
   IntrusiveHeap<DelayedWakeup> delayed_wakeup_queue_;
 
-  // This lock guards only |newly_updatable_|.  It's not expected to be heavily
-  // contended.
-  base::Lock newly_updatable_lock_;
-  std::vector<internal::TaskQueueImpl*> newly_updatable_;
-
-  // Set of task queues with avaliable work on the incoming queue.  This should
-  // only be accessed from the main thread.
-  std::set<internal::TaskQueueImpl*> updatable_queue_set_;
-
-  Observer* observer_;  // NOT OWNED.
+  Observer* const observer_;  // NOT OWNED.
 
   base::ThreadChecker main_thread_checker_;