Revert of Move throttling of background timers into the renderer scheduler

components/scheduler/base/time_domain.h

Index: components/scheduler/base/time_domain.h
diff --git a/components/scheduler/base/time_domain.h b/components/scheduler/base/time_domain.h
index 5cf39b709d11c09c47564c78a3f849565f6e7430..476a68eb5f4299f78b66d2b069fef24320a1b37a 100644
--- a/components/scheduler/base/time_domain.h
+++ b/components/scheduler/base/time_domain.h
@@ -23,24 +23,9 @@
 class TaskQueueManager;
 class TaskQueueManagerDelegate;
 
-class SCHEDULER_EXPORT TimeDomain {
+class SCHEDULER_EXPORT TimeDomain : public base::RefCounted<TimeDomain> {
  public:
-  class SCHEDULER_EXPORT Observer {
-   public:
-    virtual ~Observer() {}
-
-    // Called when an empty TaskQueue registered with this TimeDomain has a task
-    // enqueued.
-    virtual void OnTimeDomainHasImmediateWork() = 0;
-
-    // Called when a TaskQueue registered with this TimeDomain has a delayed
-    // task enqueued and no other delayed tasks associated with this TimeDomain
-    // are pending.
-    virtual void OnTimeDomainHasDelayedWork() = 0;
-  };
-
-  explicit TimeDomain(Observer* observer);
-  virtual ~TimeDomain();
+  TimeDomain();
 
   // Returns a LazyNow that evaluate this TimeDomain's Now.  Can be called from
   // any thread.
@@ -61,6 +46,9 @@
  protected:
   friend class internal::TaskQueueImpl;
   friend class TaskQueueManager;
+  friend class base::RefCounted<TimeDomain>;
+
+  virtual ~TimeDomain();
 
   void AsValueInto(base::trace_event::TracedValue* state) const;
 
@@ -81,9 +69,6 @@
   void ScheduleDelayedWork(internal::TaskQueueImpl* queue,
                            base::TimeTicks delayed_run_time,
                            LazyNow* lazy_now);
-
-  // Registers the |queue|.
-  void RegisterQueue(internal::TaskQueueImpl* queue);
 
   // Removes |queue| from the set of task queues that UpdateWorkQueues calls
   // UpdateWorkQueue on.
@@ -130,10 +115,6 @@
   // only be accessed from the main thread.
   std::set<internal::TaskQueueImpl*> updatable_queue_set_;
 
-  std::set<internal::TaskQueueImpl*> registered_task_queues_;
-
-  Observer* observer_;
-
   base::ThreadChecker main_thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(TimeDomain);