Add TaskScheduler.NumTasksBeforeDetach.[worker pool name] histogram.

base/task_scheduler/scheduler_worker_pool_impl_unittest.cc

Index: base/task_scheduler/scheduler_worker_pool_impl_unittest.cc
diff --git a/base/task_scheduler/scheduler_worker_pool_impl_unittest.cc b/base/task_scheduler/scheduler_worker_pool_impl_unittest.cc
index 0f8475a69051fc7f56a1d5d3f3feb1d4a6a75f39..5ec2942eb84751507c2f0147068dc0dd65c4234c 100644
--- a/base/task_scheduler/scheduler_worker_pool_impl_unittest.cc
+++ b/base/task_scheduler/scheduler_worker_pool_impl_unittest.cc
@@ -593,7 +593,10 @@ class TaskSchedulerWorkerPoolHistogramTest
  protected:
   void SetUp() override {}
 
-  void TearDown() override { worker_pool_->JoinForTesting(); }
+  void TearDown() override {
+    if (worker_pool_)

[robliao, 2016/10/13 18:04:04]

Mention that worker pool initialization is handled by the specific test instead
of the test case.

Can be done later: It would be nice if we could move initialization to test case
SetUp.

[fdoray, 2016/10/13 20:38:53]

Done
The problem with that is that now all test cases initialize the worker pool with
the same params. I don't know how to have code in SetUp() that behaves
differently depending on the test case.

+      worker_pool_->JoinForTesting();
+  }
 
  private:
   std::unique_ptr<StatisticsRecorder> statistics_recorder_ =
@@ -723,5 +726,44 @@ TEST_F(TaskSchedulerWorkerPoolHistogramTest, NumTasksBetweenWaitsWithDetach) {
   worker_pool_->DisallowWorkerDetachmentForTesting();
 }
 
+TEST_F(TaskSchedulerWorkerPoolHistogramTest, NumTasksBeforeDetach) {
+  InitializeWorkerPool(kReclaimTimeForDetachTests, kNumWorkersInWorkerPool);
+  auto task_runner = worker_pool_->CreateTaskRunnerWithTraits(
+      TaskTraits(), ExecutionMode::SINGLE_THREADED);
+  auto other_task_runner = worker_pool_->CreateTaskRunnerWithTraits(
+      TaskTraits(), ExecutionMode::SINGLE_THREADED);
+
+  // Post 3 tasks and wait until they run.
+  task_runner->PostTask(FROM_HERE, Bind(&DoNothing));
+  task_runner->PostTask(FROM_HERE, Bind(&DoNothing));
+  task_runner->PostTask(FROM_HERE, Bind(&DoNothing));
+  worker_pool_->WaitForAllWorkersIdleForTesting();
+
+  // To allow the SchedulerWorker associated with |task_runner| to detach:
+  // - Make sure it isn't on top of the idle stack by waking up another
+  //   SchedulerWorker.
+  // - Release |task_runner|.
+  other_task_runner->PostTask(FROM_HERE, Bind(&DoNothing));
+  task_runner = nullptr;
+
+  // Allow the SchedulerWorker to detach.
+  PlatformThread::Sleep(kReclaimTimeForDetachTests + kExtraTimeToWaitForDetach);
+
+  // Join the SchedulerWorkerPool. This forces SchedulerWorkers that detached
+  // during the test to record to the histogram.
+  worker_pool_->WaitForAllWorkersIdleForTesting();
+  worker_pool_->DisallowWorkerDetachmentForTesting();
+  worker_pool_->JoinForTesting();
+  const auto* histogram =
+      worker_pool_->num_tasks_before_detach_histogram_for_testing();
+  other_task_runner = nullptr;
+  worker_pool_.reset();
+
+  // Verify that counts were recorded to the histogram as expected.
+  EXPECT_EQ(0, histogram->SnapshotSamples()->GetCount(0));
+  EXPECT_EQ(1, histogram->SnapshotSamples()->GetCount(3));
+  EXPECT_EQ(0, histogram->SnapshotSamples()->GetCount(10));
+}
+
 }  // namespace internal
 }  // namespace base