As discussed on the mesa-dev list, the Intel Mesa driver (as of Mesa 8.0) wrongly returns GL_MAX_SAMPLES>0 even though the correct value is 0 (does not support msaa FBOs). That's causing a test failure in https://www.khronos.org/registry/webgl/conformance-suites/1.0.1/conformance/context/context-attributes-alpha-depth-stencil-antialias.html which is actually the very last 1.0.1 test failure. Setting webgl.msaa-level=0 does now give a full pass, and as we already have a full pass on NVIDIA 302.17, it's worth doing a little workaround to get that second full pass we need to claim conformance on Linux. So let's assume that Intel Mesa never supports msaa FBOs, until further notice. I asked mesa devs if it's already fixed in trunk; if it is, we'll do a version check instead.
Created attachment 648034 [details] [diff] [review] block msaa on Intel
Created attachment 648037 [details] [diff] [review] block msaa on Intel on Mesa < 8.1
Ken from the mesa-dev list confirmed that this is fixed in versions >= 8.1.0.