Admin bar shouldn't use dynamic styles on frontend for logged out visitors

[dimadin]

Admin bar gets styles depending on current user's browser. Problem is that when you using admin bar on front end for logged out users with full page cache turned on, visitor with IE or mobile might be the first one so everyone else with get that specific style.

See #26221 for similar problem.

[toscho]

That’s a general problem in WordPress: a header Vary: User-Agent is never set when the output depends on the user agent.

[DrewAPicture]

As this is not a regression, let's take a look at this in 4.1. Punting.

[sabernhardt]

28117.1.patch​ refreshes the conditional statement (Internet Explorer classes were removed in changeset 47771).

Also, I removed the nojq class from the PHP because the script no longer removes it.

[sabernhardt]

28117.1.patch still applies, but I have not tested it properly with a caching plugin.

A good testing procedure could help, and below is a basic outline (I'm sure I have missed something):

• Before applying the patch, we would want to set up page caching, then visit on a mobile device and verify the 'mobile' class is used, then visit again on a desktop and see that the class is still there.
• After applying the patch, purge the cache, then visit on mobile again to save the mobile version, and visit on a desktop to verify that it does not show the mobile version.