Revert of Move throttling of background timers into the renderer scheduler

components/scheduler/base/time_domain.cc

Index: components/scheduler/base/time_domain.cc
diff --git a/components/scheduler/base/time_domain.cc b/components/scheduler/base/time_domain.cc
index e64b4e92244fc45f62bfe19279053e84531aa0f8..2abfb522ce86f0d788285b03eb3127d4f1f56de9 100644
--- a/components/scheduler/base/time_domain.cc
+++ b/components/scheduler/base/time_domain.cc
@@ -12,21 +12,11 @@
 
 namespace scheduler {
 
-TimeDomain::TimeDomain(Observer* observer) : observer_(observer) {}
+TimeDomain::TimeDomain() {}
 
-TimeDomain::~TimeDomain() {
-  for (internal::TaskQueueImpl* queue : registered_task_queues_) {
-    queue->SetTimeDomain(nullptr);
-  }
-}
-
-void TimeDomain::RegisterQueue(internal::TaskQueueImpl* queue) {
-  registered_task_queues_.insert(queue);
-}
+TimeDomain::~TimeDomain() {}
 
 void TimeDomain::UnregisterQueue(internal::TaskQueueImpl* queue) {
-  registered_task_queues_.erase(queue);
-
   // We need to remove |task_queue| from delayed_wakeup_multimap_ which is a
   // little awkward since it's keyed by time. O(n) running time.
   for (DelayedWakeupMultimap::iterator iter = delayed_wakeup_multimap_.begin();
@@ -49,9 +39,6 @@
 
 void TimeDomain::MigrateQueue(internal::TaskQueueImpl* queue,
                               TimeDomain* destination_time_domain) {
-  DCHECK(destination_time_domain);
-  registered_task_queues_.erase(queue);
-
   LazyNow destination_lazy_now = destination_time_domain->CreateLazyNow();
   // We need to remove |task_queue| from delayed_wakeup_multimap_ which is a
   // little awkward since it's keyed by time. O(n) running time.
@@ -73,8 +60,6 @@
   // MoveNewlyUpdatableQueuesIntoUpdatableQueueSet to flush it out.
   MoveNewlyUpdatableQueuesIntoUpdatableQueueSet();
   updatable_queue_set_.erase(queue);
-
-  destination_time_domain->RegisterQueue(queue);
 }
 
 void TimeDomain::ScheduleDelayedWork(internal::TaskQueueImpl* queue,
@@ -82,26 +67,18 @@
                                      LazyNow* lazy_now) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
 
-  bool delayed_wakeup_multimap_was_empty = delayed_wakeup_multimap_.empty();
-  if (delayed_wakeup_multimap_was_empty ||
+  if (delayed_wakeup_multimap_.empty() ||
       delayed_run_time < delayed_wakeup_multimap_.begin()->first) {
     base::TimeDelta delay =
         std::max(base::TimeDelta(), delayed_run_time - lazy_now->Now());
     RequestWakeup(lazy_now, delay);
   }
-
-  if (observer_ && delayed_wakeup_multimap_was_empty)
-    observer_->OnTimeDomainHasDelayedWork();
   delayed_wakeup_multimap_.insert(std::make_pair(delayed_run_time, queue));
 }
 
 void TimeDomain::RegisterAsUpdatableTaskQueue(internal::TaskQueueImpl* queue) {
-  {
-    base::AutoLock lock(newly_updatable_lock_);
-    newly_updatable_.push_back(queue);
-  }
-  if (observer_)
-    observer_->OnTimeDomainHasImmediateWork();
+  base::AutoLock lock(newly_updatable_lock_);
+  newly_updatable_.push_back(queue);
 }
 
 void TimeDomain::UnregisterAsUpdatableTaskQueue(