Steps to reproduce:
1. Download and open the user project in GitHub (https://github.com/qCring/UnityWebGLAATest)
2. Build for WebGL
3. Open "about:config" in Firefox and disable "webgl.enable-webgl2"
4. Open generated html in Firefox
5. Notice that the cube is not affected by Anti-Aliasing

Expected result: Anti-Aliasing should be present in WebGL builds

Reproduced in: 2017.2.0b2, 2017.1.0f3, 5.6.2p2, 5.6.0a2
Not reproduced in: 5.5.4p1, 5.4.5p4
Regression since: 5.6.0a2

Fixed in: 2017.3.0a4