cancel-download.java

class AppDownload {
    WebExtension.DownloadItem mExtensionDownload;

    // Cancels the download
    GeckoResult<Void> cancel() {
        // Actually cancel the download

        // Notifies extension
        DownloadItemUpdate update = mExtensionDownload.updateCanceled(true).commit();
        DownloadItemUpdate.Builder b = new DownloadItem.Builder(mExtensionDownload, update);
        mExtensionDownload = b.build();

        return GeckoResult.fromValue(Void);
    }

    void setDownloadItem(DownloadItem item) {
        mExtensionDownload = item;
    }
}

class AppDownloadController {
    // stuff ...

    @Override
    GeckoResult<Void> onCancel(DownloadItem item, WebExtension extension) {
        AppDownload download = mDownloads.byDownloadItem(item);
        // Update the download item in case it's out of date
        download.setDownloadItem(item);
        return download.cancel();
    }
}

// UI Code

    onClick() {
        mDownload.cancel();
}