Sanitize headers in Proxy Authentication Required responses

BUG=431504

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

Cr-Commit-Position: refs/heads/master@{#310014}
bool HttpProxyClientSocket::GetSSLInfo(SSLInfo* ssl_info) {
  if (transport_.get() && transport_->socket()) {
    return transport_->socket()->GetSSLInfo(ssl_info);
  }
  NOTREACHED();
  return false;
}

bool HttpProxyClientSocket::GetSSLInfo(SSLInfo* ssl_info) {
  if (transport_.get() && transport_->socket()) {
    return transport_->socket()->GetSSLInfo(ssl_info);
  }
  NOTREACHED();
  return false;
}
