@Nullable
    public Bitmap getSmallIconBitmap() throws RemoteException {
        return mService.getSmallIconBitmap()
                .getParcelable(TrustedWebActivityService.KEY_SMALL_ICON_BITMAP);
    }
Requests a bitmap of a small icon to be used for the notification
small icon. The bitmap is decoded on the side of Trusted Web Activity client using
the resource id from {@link TrustedWebActivityService#getSmallIconId}.
@return {@link SmallIconData} with both an id and a bitmap
@throws RemoteException If the Service dies while responding to the request.
@throws SecurityException If verification with the TrustedWebActivityService fails.
customtabs/src/android/support/customtabs/trusted/TrustedWebActivityServiceWrapper.java