Enable HistoryModelWorker by default, now that bug 69561 is fixed.

BUG=69561
TEST=Run sync manually and run integration tests, sync should not crash.

Review URL: http://codereview.chromium.org/7016007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@85211 0039d316-1c4b-4281-b951-d872f2087c98
void SyncBackendHost::Core::DoStartSyncing() {
  DCHECK(MessageLoop::current() == host_->core_thread_.message_loop());
  syncapi_->StartSyncingNormally();
  if (deferred_nudge_for_cleanup_requested_)
    syncapi_->RequestNudge(FROM_HERE);
  deferred_nudge_for_cleanup_requested_ = false;
}

void SyncBackendHost::Core::DoStartSyncing() {
  DCHECK(MessageLoop::current() == host_->core_thread_.message_loop());
  syncapi_->StartSyncingNormally();
  if (deferred_nudge_for_cleanup_requested_)
    syncapi_->RequestNudge(FROM_HERE);
  deferred_nudge_for_cleanup_requested_ = false;
}
