[Sync] Add logging to diagnose SingleClientSessionsSyncTest.CookieJarMismatch flakines

I'm logging contents of FakeServer before the call to UpdateCookieJarAccountsAndWait
to ensure that later call to NavigateTab will indeed trigger commit.

I'm adding logging of last commit message to ensure that navigation to kURL2
triggered sync cycle.

R=pnoland@chromium.org
BUG=789129

Change-Id: I7adb3750f5aa2c5e4611fc32b37df461dc744d49
Reviewed-on: https://chromium-review.googlesource.com/823562
Reviewed-by: Patrick Noland <pnoland@google.com>
Commit-Queue: Pavel Yatsuk <pavely@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523818}
2 files changed