Disabling `HeapThreadDeathTest.PersistentSameThreadCheck`.

This test timed out twice this afternoon ([1], [2]). The flake portal shows
a number of other instances.

[1]: https://ci.chromium.org/p/chromium/builders/ci/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/36103
[2]: https://ci.chromium.org/p/chromium/builders/ci/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/36104
[3]: https://analysis.chromium.org/p/chromium/flake-portal/flakes/occurrences?key=ag9zfmZpbmRpdC1mb3ItbWVyUwsSBUZsYWtlIkhjaHJvbWl1bUBibGlua19oZWFwX3VuaXR0ZXN0c0BIZWFwVGhyZWFkRGVhdGhUZXN0Lk1hcmtpbmdTYW1lVGhyZWFkQ2hlY2sM&show_all_occurrences=1

TBR=kouhei@chromium.org

Bug: 993148
Change-Id: I89ae866fbfb39e96485a5692c8e4c9cf555313f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1913407Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714910}

third_party/blink/renderer/platform/heap/heap_thread_test.cc

@@ -199,16 +199,14 @@ class MarkingSameThreadCheckTester : public AlternatingThreadTester {
 };
 
 #if DCHECK_IS_ON()
-// TODO(keishi) This test is flaky on mac-rel bot.
-// crbug.com/709069
-#if !defined(OS_MACOSX)
-TEST_F(HeapThreadDeathTest, MarkingSameThreadCheck) {
+// TODO(keishi) This test is flaky on mac-rel bot. https://crbug.com/709069, and
+// times out on other bots. https://crbug.com/993148.
+TEST_F(HeapThreadDeathTest, DISABLED_MarkingSameThreadCheck) {
   // This will crash during marking, at the DCHECK in Visitor::markHeader() or
   // earlier.
   EXPECT_DEATH(MarkingSameThreadCheckTester().Test(), "");
 }
 #endif
-#endif
 
 class DestructorLockingObject
     : public GarbageCollected<DestructorLockingObject> {