TaskScheduler: Stop checking is_running_task when entering/exiting blocking calls.

Previously, we had logic to avoid handling ScopedBlockingCalls
outside of blocking tasks. This logic is redundant now that the
WaitableEvents used by SchedulerWorkers are marked as
"only used while idle"
(https://chromium-review.googlesource.com/c/chromium/src/+/1305891/22/base/task/task_scheduler/scheduler_worker.cc)

Change-Id: Ie349c868dc89b0e806c9d22937cd95b4e06c5824
Reviewed-on: https://chromium-review.googlesource.com/c/1450044
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628447}

base/task/task_scheduler/scheduler_worker_pool_impl.cc

@@ -840,10 +840,7 @@ void SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::OnMainExit(
 void SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::BlockingStarted(
     BlockingType blocking_type) {
   DCHECK_CALLED_ON_VALID_THREAD(worker_thread_checker_);
-
-  // Blocking calls made outside of tasks should not influence the max tasks.
-  if (!worker_only().is_running_task)
-    return;
+  DCHECK(worker_only().is_running_task);
 
   switch (blocking_type) {
     case BlockingType::MAY_BLOCK:
@@ -858,6 +855,7 @@ void SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::BlockingStarted(
 void SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::
     BlockingTypeUpgraded() {
   DCHECK_CALLED_ON_VALID_THREAD(worker_thread_checker_);
+  DCHECK(worker_only().is_running_task);
 
   {
     AutoSchedulerLock auto_lock(outer_->lock_);
@@ -882,10 +880,7 @@ void SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::
 
 void SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::BlockingEnded() {
   DCHECK_CALLED_ON_VALID_THREAD(worker_thread_checker_);
-
-  // Ignore blocking calls made outside of tasks.
-  if (!worker_only().is_running_task)
-    return;
+  DCHECK(worker_only().is_running_task);
 
   AutoSchedulerLock auto_lock(outer_->lock_);
   if (incremented_max_tasks_since_blocked_) {
@@ -904,6 +899,7 @@ void SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::BlockingEnded() {
 
 void SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::MayBlockEntered() {
   DCHECK_CALLED_ON_VALID_THREAD(worker_thread_checker_);
+  DCHECK(worker_only().is_running_task);
 
   bool must_schedule_adjust_max_tasks = false;
   {
@@ -925,6 +921,7 @@ void SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::MayBlockEntered() {
 
 void SchedulerWorkerPoolImpl::SchedulerWorkerDelegateImpl::WillBlockEntered() {
   DCHECK_CALLED_ON_VALID_THREAD(worker_thread_checker_);
+  DCHECK(worker_only().is_running_task);
 
   bool must_schedule_adjust_max_tasks = false;
   SchedulerWorkerActionExecutor executor(outer_);