Send Post request along with HttpHeaders on Android

I need to post data to server (with "referer" header field) and load the response in Webview.

Now, there are different methods (from Android WebView) to do parts of it, like there is:

void loadUrl(String url, Map<String, String> additionalHttpHeaders)

Loads the given URL with the specified additional HTTP headers.

void loadData(String data, String mimeType, String encoding)

Loads the given data into this WebView using a 'data' scheme URL.

void postUrl(String url, byte[] postData)

Loads the URL with postData using "POST" method into this WebView.

loadUrl() allows to send HttpHeaders but doesn't allow to send post data, other methods seem to be not allowing to send HttpHeaders. Am I missing something or what I am trying is not possible?