Report expected task queueing time via UMA

components/scheduler/base/task_queue_manager.h

 // 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.
 
 #ifndef CONTENT_RENDERER_SCHEDULER_BASE_TASK_QUEUE_MANAGER_H_
 #define CONTENT_RENDERER_SCHEDULER_BASE_TASK_QUEUE_MANAGER_H_
 
 #include <map>
 
 #include "base/atomic_sequence_num.h"
@@ skipping 20 matching lines @@
 
 namespace scheduler {
 namespace internal {
 class TaskQueueImpl;
 }  // namespace internal
 
 class LazyNow;
 class RealTimeDomain;
 class TimeDomain;
 class TaskQueueManagerDelegate;
+class TaskTimeTracker;
 
 // The task queue manager provides N task queues and a selector interface for
 // choosing which task queue to service next. Each task queue consists of two
 // sub queues:
 //
 // 1. Incoming task queue. Tasks that are posted get immediately appended here.
 //    When a task is appended into an empty incoming queue, the task manager
 //    work function (DoWork) is scheduled to run on the main task runner.
 //
 // 2. Work queue. If a work queue is empty when DoWork() is entered, tasks from
@@ skipping 24 matching lines @@
   void MaybeScheduleDelayedWork(const tracked_objects::Location& from_here,
                                 base::TimeTicks now,
                                 base::TimeDelta delay);
 
   // Set the number of tasks executed in a single invocation of the task queue
   // manager. Increasing the batch size can reduce the overhead of yielding
   // back to the main message loop -- at the cost of potentially delaying other
   // tasks posted to the main loop. The batch size is 1 by default.
   void SetWorkBatchSize(int work_batch_size);
 
+  void SetTaskTimeTracker(TaskTimeTracker* task_time_tracker) {

[alex clarke (OOO till 29th), 2016/07/06 09:51:39]

Please add a brief comment explaining what happens if a TaskTimeTracker is
added.  Please also document that it must outlive the TQM (or be removed by
calling SetTaskTimeTracker(nullptr).

[tdresser, 2016/07/06 13:25:34]

Done.

+    task_time_tracker_ = task_time_tracker;
+  }
+
   // These functions can only be called on the same thread that the task queue
   // manager executes its tasks on.
   void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer);
   void RemoveTaskObserver(base::MessageLoop::TaskObserver* task_observer);
 
   // Returns true if any task from a monitored task queue was was run since the
   // last call to GetAndClearSystemIsQuiescentBit.
   bool GetAndClearSystemIsQuiescentBit();
 
   // Creates a task queue with the given |spec|.  Must be called on the thread
@@ skipping 65 matching lines @@
 
   // Use the selector to choose a pending task and run it.
   void DoWork(base::TimeTicks run_time, bool from_main_thread);
 
   // Delayed Tasks with run_times <= Now() are enqueued onto the work queue.
   // Reloads any empty work queues which have automatic pumping enabled and
   // which are eligible to be auto pumped based on the |previous_task| which was
   // run and |should_trigger_wakeup|. Call with an empty |previous_task| if no
   // task was just run.
   void UpdateWorkQueues(bool should_trigger_wakeup,
-                        const internal::TaskQueueImpl::Task* previous_task);
+                        const internal::TaskQueueImpl::Task* previous_task,
+                        LazyNow lazy_now);
 
   // Chooses the next work queue to service. Returns true if |out_queue|
   // indicates the queue from which the next task should be run, false to
   // avoid running any tasks.
   bool SelectWorkQueueToService(internal::WorkQueue** out_work_queue);
 
   // Runs a single nestable task from the |queue|. On exit, |out_task| will
   // contain the task which was executed. Non-nestable task are reposted on the
   // run loop. The queue must not be empty.
   enum class ProcessTaskResult {
@@ skipping 38 matching lines @@
 
   base::ThreadChecker main_thread_checker_;
   scoped_refptr<TaskQueueManagerDelegate> delegate_;
   internal::TaskQueueSelector selector_;
 
   base::Closure from_main_thread_immediate_do_work_closure_;
   base::Closure from_other_thread_immediate_do_work_closure_;
 
   bool task_was_run_on_quiescence_monitored_queue_;
 
-  // To reduce locking overhead we track pending calls to DoWork seperatly for
+  // To reduce locking overhead we track pending calls to DoWork seperately for

[Sami, 2016/07/06 10:08:29]

typo: separately :)

[tdresser, 2016/07/06 13:25:34]

Done.

   // the main thread and other threads.
   std::set<base::TimeTicks> main_thread_pending_wakeups_;
 
   // Protects |other_thread_pending_wakeups_|.
   mutable base::Lock other_thread_lock_;
   std::set<base::TimeTicks> other_thread_pending_wakeups_;
 
   int work_batch_size_;
   size_t task_count_;
 
   base::ObserverList<base::MessageLoop::TaskObserver> task_observers_;
 
+  TaskTimeTracker* task_time_tracker_;  // NOT OWNED
+
   const char* tracing_category_;
   const char* disabled_by_default_tracing_category_;
   const char* disabled_by_default_verbose_tracing_category_;
 
   internal::TaskQueueImpl* currently_executing_task_queue_;  // NOT OWNED
 
   Observer* observer_;  // NOT OWNED
   scoped_refptr<DeletionSentinel> deletion_sentinel_;
   base::WeakPtrFactory<TaskQueueManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueueManager);
 };
 
 }  // namespace scheduler
 
 #endif  // CONTENT_RENDERER_SCHEDULER_BASE_TASK_QUEUE_MANAGER_H_