Add tests for passing simple ESSL3 shaders to WebGL 1

Currently, ANGLE-based browsers fail some of the tests, accepting
simple ESSL3 shaders in a WebGL 1 context.
Small fixes to the WebGL 1 ESSL3 shader test
Merge pull request #761 from NVIDIA/essl3-shader-bug-test

Add tests for passing simple ESSL3 shaders to WebGL 1