Auto merge of #17 - mmatyas:essl_support, r=emilio
Auto merge of #17 - mmatyas:essl_support, r=emilio

Enable ESSL support

This enables the ESSL validator, required for testing the shaders of servo/webrender.

ecoal95/angle,ecoal95/angle,ecoal95/angle,ecoal95/angle,ecoal95/angle