I'm getting this error repeatedly on mediawiki.org. Nothing loads at all on most attempts, and gives the above error. Sometimes, I'll get the requested page, but with no CSS at all. So far, I'm not getting the error on any other site, including the original Commons link. Exiting and restarting the browser *might* help, but that might just be a fluke.
Unlike the OP, this just started for me today or yesterday. A couple of days ago, the site was fine.
I'm using Chrome 45 on Windows 10, so it's possible this is some intermittent incompatibility introduced with Chrome 44.
Looking around some more, it seems not to be a MediaWiki specific issue at all. This reddit thread gives some insight. https://www.reddit.com/r/chrome/comments/3j1oqk/beta_or_canary_users_have_versions_later_than_44/
Given that disabling Avast temporarily seems to fix the problem, I believe it's most likely an incompatibility between Avast and Chrome, introduced in Chrome 44, and for whatever reason, mediawiki.org appears to be prone to triggering it, much like reddit is.
ERR_SPDY_PROTOCOL_ERROR is a very generic error message that basically means something went wrong with the communication with the web server while using SPDY o HTTP/2. That could be a browser bug, an Apache or Varnish bug, a web server configuration problem, whatever.
If the error still occurs and you can reproduce it with some reliability, I think the way forward is to log the network details as described here and file a bug with those details attached against the Chromium project; they can at least figure out what the exact protocol problem is.
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