Revert "[User events] Re-enable a previously flaky test"

This reverts commit 7231941c.

Reason for revert: It is indeed flaky, this provided some insights, reverting.

Original change's description:
> [User events] Re-enable a previously flaky test
> 
> This CL re-enables a previously flaky test. If still flaky, the goal is
> to gather failure logs to understand the root cause (logging has
> improved substantially since this test got disabled).
> 
> Bug: 1006155
> Change-Id: I384bbb3cf83068a6d1297592b9400a8ffe23ff73
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2031035
> Auto-Submit: Jan Krcal <jkrcal@chromium.org>
> Commit-Queue: Marc Treib <treib@chromium.org>
> Reviewed-by: Marc Treib <treib@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#737266}

TBR=treib@chromium.org,jkrcal@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1006155
Change-Id: Ib59c61ffd0feae55d6db156e79c06f283c4ca41c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2035413Reviewed-by: Jan Krcal <jkrcal@chromium.org>
Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737761}

chrome/browser/sync/test/integration/single_client_user_events_sync_test.cc

@@ -89,7 +89,13 @@ IN_PROC_BROWSER_TEST_F(SingleClientUserEventsSyncTest, RetrySequential) {
   EXPECT_TRUE(ExpectUserEvents({specifics1, specifics1, specifics2}));
 }
 
-IN_PROC_BROWSER_TEST_F(SingleClientUserEventsSyncTest, RetryParallel) {
+// Flaky (mostly) on ASan/TSan. http://crbug.com/998130
+#if defined(ADDRESS_SANITIZER) || defined(THREAD_SANITIZER)
+#define MAYBE_RetryParallel DISABLED_RetryParallel
+#else
+#define MAYBE_RetryParallel RetryParallel
+#endif
+IN_PROC_BROWSER_TEST_F(SingleClientUserEventsSyncTest, MAYBE_RetryParallel) {
   ASSERT_TRUE(SetupSync());
 
   const UserEventSpecifics specifics1 =