Report expected task queueing time via UMA

components/scheduler/base/task_queue_manager.cc

Index: components/scheduler/base/task_queue_manager.cc
diff --git a/components/scheduler/base/task_queue_manager.cc b/components/scheduler/base/task_queue_manager.cc
index 36f08de540fe8529ab593f6248504b0d23561795..9e7192fc84e03250986f5be29b0b9ac5613daa62 100644
--- a/components/scheduler/base/task_queue_manager.cc
+++ b/components/scheduler/base/task_queue_manager.cc
@@ -14,6 +14,7 @@
 #include "components/scheduler/base/task_queue_impl.h"
 #include "components/scheduler/base/task_queue_manager_delegate.h"
 #include "components/scheduler/base/task_queue_selector.h"
+#include "components/scheduler/base/task_time_tracker.h"
 #include "components/scheduler/base/work_queue.h"
 #include "components/scheduler/base/work_queue_sets.h"
 
@@ -38,12 +39,14 @@ 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)
     : real_time_domain_(new RealTimeDomain(tracing_category)),
       delegate_(delegate),
       task_was_run_on_quiescence_monitored_queue_(false),
       work_batch_size_(1),
       task_count_(0),
+      task_time_tracker_(task_time_tracker),
       tracing_category_(tracing_category),
       disabled_by_default_tracing_category_(
           disabled_by_default_tracing_category),
@@ -192,6 +195,10 @@ void TaskQueueManager::DoWork(base::TimeTicks run_time, bool from_main_thread) {
   UpdateWorkQueues(false, nullptr);
 
   internal::TaskQueueImpl::Task previous_task;
+  base::TimeTicks task_start_time;
+  if (!delegate_->IsNested() && from_main_thread)
+    task_start_time = real_time_domain()->Now();

[alex clarke (OOO till 29th), 2016/07/05 14:59:35]

UpdateWorkQueues can also call real_time_domain()->Now(). It might be nice to
refactor it to remove the duplication.  It's probably cleanest to pass
task_start_time in to UpdateWorkQueues.

[tdresser, 2016/07/05 15:52:20]

Done.

+
   for (int i = 0; i < work_batch_size_; i++) {
     internal::WorkQueue* work_queue;
     if (!SelectWorkQueueToService(&work_queue)) {
@@ -200,6 +207,7 @@ void TaskQueueManager::DoWork(base::TimeTicks run_time, bool from_main_thread) {
 
     bool should_trigger_wakeup = work_queue->task_queue()->wakeup_policy() ==
                                  TaskQueue::WakeupPolicy::CAN_WAKE_OTHER_QUEUES;
+
     switch (ProcessTaskFromWorkQueue(work_queue, &previous_task)) {
       case ProcessTaskResult::DEFERRED:
         // If a task was deferred, try again with another task. Note that this
@@ -211,6 +219,13 @@ void TaskQueueManager::DoWork(base::TimeTicks run_time, bool from_main_thread) {
       case ProcessTaskResult::TASK_QUEUE_MANAGER_DELETED:
         return;  // The TaskQueueManager got deleted, we must bail out.
     }
+    if (!delegate_->IsNested() && from_main_thread) {
+      // Only report top level task durations.
+      base::TimeTicks task_end_time = real_time_domain()->Now();
+      task_time_tracker_->ReportTaskTime(task_start_time, task_end_time);
+      task_start_time = task_end_time;
+    }
+
     work_queue = nullptr; // The queue may have been unregistered.
 
     UpdateWorkQueues(should_trigger_wakeup, &previous_task);