public boolean requestPostMessageChannel(Uri postMessageOrigin) {
        Bundle extras = new Bundle();
        addIdToBundle(extras);
        try {
            return mService.requestPostMessageChannelWithExtras(
                    mCallback, postMessageOrigin, extras);
        } catch (RemoteException e) {
            return false;
        }
    }
Sends a request to create a two way postMessage channel between the client and the browser.

@param postMessageOrigin      A origin that the client is requesting to be identified as
                              during the postMessage communication.
@return Whether the implementation accepted the request. Note that returning true
        here doesn't mean an origin has already been assigned as the validation is
        asynchronous.
customtabs/src/android/support/customtabs/CustomTabsSession.java