Don't wrap the main thread when running death tests.

Also re-enable the TestAnnotationsOnWrongQueueDebug test and rename
the test suite to SequenceCheckerDeathTest so that it gets executed
before other tests.

Bug: webrtc:11577
Change-Id: I3b8037644e4b9139755ccecb17e42b09327e4996
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/175346
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31290}

rtc_base/synchronization/sequence_checker_unittest.cc

@@ -158,8 +158,12 @@ void TestAnnotationsOnWrongQueue() {
 }
 
 #if RTC_DCHECK_IS_ON
-// TODO(bugs.webrtc.org/11577): Fix flakiness.
-TEST(SequenceCheckerTest, DISABLED_TestAnnotationsOnWrongQueueDebug) {
+// Note: Ending the test suite name with 'DeathTest' is important as it causes
+// gtest to order this test before any other non-death-tests, to avoid potential
+// global process state pollution such as shared worker threads being started
+// (e.g. a side effect of calling InitCocoaMultiThreading() on Mac causes one or
+// two additional threads to be created).
+TEST(SequenceCheckerDeathTest, TestAnnotationsOnWrongQueueDebug) {
   ASSERT_DEATH({ TestAnnotationsOnWrongQueue(); }, "");
 }
 #else