Fix MessageLoopTest.DeleteUnboundLoop with SequenceManager

Currently the SequenceManager is being too restrictive for this
test, so we relax our check slightly.

Bug: 891670
Change-Id: I0cebd070971e0272624b7bd05165ec64404b8f1a
Reviewed-on: https://chromium-review.googlesource.com/c/1357080
Commit-Queue: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612701}

base/task/sequence_manager/task_queue_impl.cc

@@ -621,7 +621,8 @@ void TaskQueueImpl::SetTimeDomain(TimeDomain* time_domain) {
 }
 
 TimeDomain* TaskQueueImpl::GetTimeDomain() const {
-  DCHECK(associated_thread_->IsBoundToCurrentThread());
+  DCHECK(associated_thread_->IsBoundToCurrentThread() ||
+         !associated_thread_->IsBound());
   return main_thread_only().time_domain;
 }