Disable flaky TwoClientPollingSyncTest.ShouldPollOnStartup

Bug: 988161
Change-Id: I911dc2a215646fccac401d1b76324531cb59d42a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1738369
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Auto-Submit: Marc Treib <treib@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684308}

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

@@ -68,7 +68,8 @@ class SessionCountMatchChecker : public SingleClientStatusChangeChecker {
 // In the second phase, we take down client 1 and while it's down upload more
 // data from client 0. That second phase will rely on polling on client 1 to
 // receive the update.
-IN_PROC_BROWSER_TEST_F(TwoClientPollingSyncTest, ShouldPollOnStartup) {
+// Flaky: crbug.com/988161
+IN_PROC_BROWSER_TEST_F(TwoClientPollingSyncTest, DISABLED_ShouldPollOnStartup) {
   ASSERT_TRUE(SetupClients()) << "SetupClients() failed.";
 
   // Choose larger interval to verify the poll-on-start logic.