Remove Cardboard middle white line

[Vamoss]

Hi, we are looking for a way to remove the white line in the CardboardUI, in some cases were the cardboard does not fit perfectly to the smartphone, this lines interferes in the user experience.

I understand the CardboardUI is a complex shader, but if we expose the kCenterLineThicknessDp variable, we can attribute a zero value to it:

webvr-polyfill/build/webvr-polyfill.js

Line 1245 in ceb80d0

var kCenterLineThicknessDp = 4;

Cheers,
Carlos