[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}

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

@@ -89,13 +89,7 @@ IN_PROC_BROWSER_TEST_F(SingleClientUserEventsSyncTest, RetrySequential) {
   EXPECT_TRUE(ExpectUserEvents({specifics1, specifics1, specifics2}));
 }
 
-// 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) {
+IN_PROC_BROWSER_TEST_F(SingleClientUserEventsSyncTest, RetryParallel) {
   ASSERT_TRUE(SetupSync());
 
   const UserEventSpecifics specifics1 =