Report expected task queueing time via UMA

components/scheduler/base/task_queue_manager.h

Index: components/scheduler/base/task_queue_manager.h
diff --git a/components/scheduler/base/task_queue_manager.h b/components/scheduler/base/task_queue_manager.h
index 1e9eef4d2819447ae41d96387b56857ee5519f91..a61a2cdc6ce563892c957cfdc41f990541844aca 100644
--- a/components/scheduler/base/task_queue_manager.h
+++ b/components/scheduler/base/task_queue_manager.h
@@ -38,6 +38,7 @@ 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
@@ -60,7 +61,8 @@ class SCHEDULER_EXPORT TaskQueueManager
   TaskQueueManager(scoped_refptr<TaskQueueManagerDelegate> delegate,
                    const char* tracing_category,
                    const char* disabled_by_default_tracing_category,
-                   const char* disabled_by_default_verbose_tracing_category);
+                   const char* disabled_by_default_verbose_tracing_category,
+                   TaskTimeTracker* task_time_tracker);

[Sami, 2016/07/05 14:40:39]

Could you make this optional (e.g., SetTaskTimeTracker). That would let use
avoid doing unneeded measurements (e.g., on worker threads).

[tdresser, 2016/07/05 20:09:38]

Done.

   ~TaskQueueManager() override;
 
   // Requests that a task to process work is posted on the main task runner.
@@ -239,6 +241,9 @@ class SCHEDULER_EXPORT TaskQueueManager
 
   base::ObserverList<base::MessageLoop::TaskObserver> task_observers_;
 
+  TaskTimeTracker* task_time_tracker_;  // NOT OWNED
+  int do_work_depth_;
+
   const char* tracing_category_;
   const char* disabled_by_default_tracing_category_;
   const char* disabled_by_default_verbose_tracing_category_;