Enable QUIC support in chromoting

- Added GetQuicChannelFactory() in JingleSession, so now it's possible
  to create channels over QUIC.
- SessionConfig was updated to support QUIC-based transport. PseudoTCP
  is still used by default.
- ContentDescription class is updated to exchange QuicConfig blobs
  generated by QuicChannelFactory.
- ChromotingInstance allows to enable QUIC by enabling "quic"
  experiment in the webapp.

BUG=448838

Review URL: https://codereview.chromium.org/1277093006

Cr-Commit-Position: refs/heads/master@{#343463}
28 files changed