[e] (0) Sync <picture> section with upstream content
Affected topics: DOM APIs

git-svn-id: https://svn.whatwg.org/webapps@8847 340c8d12-0b0e-0410-8428-c7bf67bfef74
[e] (0) fix a mess I made with 'referrer source' recently
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=27032
Affected topics: DOM APIs, HTML, Workers

git-svn-id: https://svn.whatwg.org/webapps@8848 340c8d12-0b0e-0410-8428-c7bf67bfef74
Merge remote branch 'origin/master' into whatwg