Sanitize headers in Proxy Authentication Required responses

BUG=431504

Review URL: https://codereview.chromium.org/769043003

Cr-Commit-Position: refs/heads/master@{#310014}
int SpdyProxyClientSocket::RestartWithAuth(const CompletionCallback& callback) {
  next_state_ = STATE_DISCONNECTED;
  return OK;
}

int SpdyProxyClientSocket::RestartWithAuth(const CompletionCallback& callback) {
  next_state_ = STATE_DISCONNECTED;
  return OK;
}
