[giow] (3) Try to fix the logic around opening new tabs because the user said so, even in sandboxed environments
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=26317
Affected topics: DOM APIs, HTML

git-svn-id: https://svn.whatwg.org/webapps@8776 340c8d12-0b0e-0410-8428-c7bf67bfef74