Access ChromotingHost::clients_ only on network thread.

Previously ChromotingHost was doing some work on the main thread and
some on the network thread. |clients_| and some other members were
accessed without lock on both of these threads. Moved most of the
ChromotingHost activity to the network thread to avoid possible
race conditions.

BUG=96325
TEST=Chromoting works

Review URL: http://codereview.chromium.org/8495024

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@109556 0039d316-1c4b-4281-b951-d872f2087c98
void ChromotingHost::ShutdownRecorder() {

void ChromotingHost::ShutdownRecorder() {
  if (MessageLoop::current() != context_->main_message_loop()) {
    context_->main_message_loop()->PostTask(
        FROM_HERE, base::Bind(&ChromotingHost::ShutdownRecorder, this));
    return;
  }
  if (recorder_.get()) {
    StopScreenRecorder();
  } else if (!stopping_recorders_) {
    ShutdownFinish();
  }
}
