Branched disucssion from https://codereview.chromium.org/2766603004. 

xunjieli@ suggests a change QuicCryptoClientStream::CryptoConnect API to make the API contract clearer as the current signature doesn't indicate that it can return error synchronously.  crbug.com/700617  is caused by failing to handle the sync error in this code.

int QuicChromiumClientSession::CryptoConnect(
    const CompletionCallback& callback) {
  connect_timing_.connect_start = base::TimeTicks::Now();
  RecordHandshakeState(STATE_STARTED);
  DCHECK(flow_controller());
  crypto_stream_->CryptoConnect();   <------- doesn't indicate could fail synchronously.

  if (IsCryptoHandshakeConfirmed()) {
    connect_timing_.connect_end = base::TimeTicks::Now();
    return OK;
  }

  // Unless we require handshake confirmation, activate the session if
  // we have established initial encryption.
  if (!require_confirmation_ && IsEncryptionEstablished())
    return OK;

  callback_ = callback;
  return ERR_IO_PENDING;
}