Revert 102184 - [Sync] use base::Time in sync

Make EntryKernel/Entry/BaseNode use base::Time instead of int64s.

Add sync/util/time.h, with utility functions to manage the sync proto
time format.

Store times on disk in proto format instead of the local system.
This requires a database version bump (to 77).

Update SessionChangeProcessor/SessionModelAssociator
to use base::Time, too.

Remove hackish Now() function.

Remove ZeroFields() function, and instead zero-initialize in EntryKernel::EntryKernel() directly.

BUG=
TEST=

Review URL: http://codereview.chromium.org/7981006

TBR=akalin@chromium.org
Review URL: http://codereview.chromium.org/7977034

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@102186 0039d316-1c4b-4281-b951-d872f2087c98
  void Observe(int type,
      const NotificationSource& source,
      const NotificationDetails& details) {
    switch (type) {
      case chrome::NOTIFICATION_FOREIGN_SESSION_UPDATED:
        notified_of_update_ = true;
        break;
      default:
        NOTREACHED();
        break;
    }
  }

  void Observe(int type,
      const NotificationSource& source,
      const NotificationDetails& details) {
    switch (type) {
      case chrome::NOTIFICATION_FOREIGN_SESSION_UPDATED:
        notified_of_update_ = true;
        break;
      default:
        NOTREACHED();
        break;
    }
  }
