GPU fill rate baseline

An ideal web-page is rendered by shading each pixel exactly once with no work done by the shader. We can estimate this case by drawing a full-screen rectangle and capturing the GPU time, which is what gl-bench tool does.

On this page, we are going to collect different numbers reported by the tool:

System	Driver	Renderer	Resolution	Avg GPU time	Time per megapixel
Linux/GLX	Mesa 17.2.4	Intel(R) HD Graphics 520 (Skylake GT2)	2560x1440	0.56	0.15