Disable flaky SingleClientSessionsSyncTest.CookieJarMismatch

Example flakes:
https://ci.chromium.org/buildbot/chromium.linux/Linux%20Tests/65337
https://ci.chromium.org/buildbot/chromium.linux/Linux%20Tests/65304
https://ci.chromium.org/buildbot/chromium.linux/Linux%20Tests/65296

BUG=799129
TBR=pavely@chromium.org

Change-Id: Id9775baf2e5f82e7c5b7a9bd3194cf24dd3ad74e
Reviewed-on: https://chromium-review.googlesource.com/822980Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523531}

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

@@ -379,7 +379,8 @@ IN_PROC_BROWSER_TEST_F(SingleClientSessionsSyncTest, SourceTabIDSet) {
 
 // TODO(pavely): This test is flaky. Report failures in
 // https://crbug.com/789129.
-IN_PROC_BROWSER_TEST_F(SingleClientSessionsSyncTest, CookieJarMismatch) {
+IN_PROC_BROWSER_TEST_F(SingleClientSessionsSyncTest,
+                       DISABLED_CookieJarMismatch) {
   ASSERT_TRUE(SetupSync()) << "SetupSync() failed.";
 
   ASSERT_TRUE(CheckInitialState(0));