Make WebRequest and GeckoWebExecutor First-Party aware

GeckoWebExecutor, and WebRequest, are only aware of the request URL, but they don't have necessary context for setting first-party origin attributes.

https://searchfox.org/mozilla-beta/source/widget/android/WebExecutorSupport.cpp#360

nsresult WebExecutorSupport::CreateStreamLoader(
    java::WebRequest::Param aRequest, int32_t aFlags,
    java::GeckoResult::Param aResult) {
  const auto req = java::WebRequest::LocalRef(aRequest);
  const auto reqBase = java::WebMessage::LocalRef(req.Cast<java::WebMessage>());

  nsCOMPtr<nsIURI> uri;
  nsresult rv = NS_NewURI(getter_AddRefs(uri), reqBase->Uri()->ToString());
  NS_ENSURE_SUCCESS(rv, NS_ERROR_MALFORMED_URI);

  nsCOMPtr<nsIChannel> channel;
  rv = NS_NewChannel(getter_AddRefs(channel), uri,
                     nsContentUtils::GetSystemPrincipal(),
                     nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_SEC_CONTEXT_IS_NULL,
                     nsIContentPolicy::TYPE_OTHER);
  NS_ENSURE_SUCCESS(rv, rv);

  if (aFlags & java::GeckoWebExecutor::FETCH_FLAGS_ANONYMOUS) {
    channel->SetLoadFlags(nsIRequest::LOAD_ANONYMOUS);
  }                                                                                                                                                                                                         

  nsCOMPtr<nsICookieJarSettings> cookieJarSettings =
      CookieJarSettings::Create();
  MOZ_ASSERT(cookieJarSettings);

  nsCOMPtr<nsILoadInfo> loadInfo = channel->LoadInfo();
  loadInfo->SetCookieJarSettings(cookieJarSettings);

  // setup http/https specific things
  nsCOMPtr<nsIHttpChannel> httpChannel(do_QueryInterface(channel, &rv));
  if (httpChannel) {
    rv = SetupHttpChannel(httpChannel, channel, aRequest);
    NS_ENSURE_SUCCESS(rv, rv);
  }

I'll open a bugzilla ticket for this, too.