I have the same issue in Chrome on OSX, and WebGL is enabled for me. I've played some of the WebGL demo games, so I doubt it's due to my GPU being blacklisted.
Though interestingly, the behavior in all three Chromes is wildly different: Dev runs 60% CPU use in the rendering process, Beta sometimes uses nothing, sometimes 60%, and Stable uses the same 60% + 120% on "google chrome helper". The alert test works (shows a canvas element) in both Dev and Beta, Stable shows me a "page unresponsive" after a couple seconds and never alerts anything.
Other GL tests work just fine in all 3. I'll be happy to test other things if you can come up with them :)
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