[blink scheduler] Convert CHECK to DCHECK in FrameSchedulerImpl::ShouldThrottleTaskQueues.

We did not receive crash reports, so we are confident that the
assertion is correct. We can convert it to a DCHECK to avoid the
overhead in production.

Fixed: 1078387
Change-Id: I5a14f215718cc1d9b12cd04f0e071094a575afe7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510776
Auto-Submit: François Doray <fdoray@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823282}

third_party/blink/renderer/platform/scheduler/main_thread/frame_scheduler_impl.cc

@@ -943,9 +943,7 @@ bool FrameSchedulerImpl::IsOrdinary() const {
 }
 
 bool FrameSchedulerImpl::ShouldThrottleTaskQueues() const {
-  // TODO(crbug.com/1078387): Convert the CHECK to a DCHECK once enough time has
-  // passed to confirm that it is correct. (November 2020).
-  CHECK(parent_page_scheduler_);
+  DCHECK(parent_page_scheduler_);
 
   if (!RuntimeEnabledFeatures::TimerThrottlingForBackgroundTabsEnabled())
     return false;