Add TaskScheduler.NumTasksBetweenWaits.[pool] histogram.

base/task_scheduler/scheduler_worker_pool_impl.h

 // Copyright 2016 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 BASE_TASK_SCHEDULER_SCHEDULER_WORKER_POOL_IMPL_H_
 #define BASE_TASK_SCHEDULER_SCHEDULER_WORKER_POOL_IMPL_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 159 matching lines @@
 
 #if DCHECK_IS_ON()
   // Signaled when all workers have been created.
   WaitableEvent workers_created_;
 #endif
 
   // TaskScheduler.DetachDuration.[worker pool name] histogram. Intentionally
   // leaked.
   HistogramBase* const detach_duration_histogram_;
 
+  // TaskScheduler.NumTasksBetweenWaits.[worker pool name] histogram.
+  // Intentionally leaked.
+  HistogramBase* const num_tasks_between_waits_histogram_;
+
   // TaskScheduler.TaskLatency.[worker pool name].[task priority] histograms.
   // Indexed by task priority. Histograms are allocated on demand to reduce
   // memory usage (some task priorities might never run in this
   // SchedulerThreadPoolImpl). Intentionally leaked.
   subtle::AtomicWord
       task_latency_histograms_[static_cast<int>(TaskPriority::HIGHEST) + 1] =
           {};
 
   TaskTracker* const task_tracker_;
   DelayedTaskManager* const delayed_task_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(SchedulerWorkerPoolImpl);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_SCHEDULER_WORKER_POOL_IMPL_H_