@ReactMethod
    public void unloadSounds(ReadableArray soundArray) {
        for (int i = 0; i < soundArray.size(); i++) {
            String keyToRemove = soundArray.getString(i);
            SoundData dataToRemove = mSoundDataMap.get(keyToRemove);
            if (dataToRemove != null) {
                dataToRemove.destroy();
                mSoundDataMap.remove(keyToRemove);
            }
        }
    }
This function takes a map of keys to sounds and creates SoundData objects
to prefetch the data before storing them in a local map. We currently only
support external urls (web-based).

@param soundMap a map of String keys to String url's.
android/viro_bridge/src/main/java/com/viromedia/bridge/module/SoundModule.java