If you don't see the flagpole, your WebGL implementation might be broken. I had to launch Chrome on a dedicated GPU (using optirun/bumblebee), it didn't work on the Intel one. A lot of stuff is logged into console, the relevant part is probably "extension `GL_ARB_gpu_shader5' unsupported in fragment shader". I guess my laptop is just too old.

Thinkpad T420, i5-2540M (didn't work) & Quadro NVS 4200M (works), Linux.