[Sync] Fix crash when all visits are from the future

It's possible for all favicons to have last visit times in the future. In that
case, adding a local favicon will result in its immediate expiration.
Previously this would crash. Now this will just result in a silent expiration
and no sync interaction.

BUG=306150

Review URL: https://codereview.chromium.org/27246002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228586 0039d316-1c4b-4281-b951-d872f2087c98
Enabled Startup and shutdown timebombs and hang/jank detection by
ThreadWatcher.

Get a crash dump if UI thread doesn't respond for 60 pings
(or 120 secs). Picked a very high number to catch the worst
hangs/janks and to have fewer crash dumps due to ThreadWatcher.

R=jar@chromium.org

Review URL: https://codereview.chromium.org/27261002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228587 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228587