However, when I use it, I get:

Error in eventhandler for browserAction.onClicked: TypeError: chrome.runtime.sendNativeMessage is not a function.

Is this a permissions issue? what am I doing wrong ?

chrome.runtime.sendNativeMessage("com.xxx.yyy", "get_zzz",
    function (response) {
        alert("message from external component: " + response);
    });