Allow WebKit browsers to break strings in `<code>` tags.
This prevents an overflow for example on Permalink Settings.

fixes #28161.
Built from https://develop.svn.wordpress.org/trunk@29501


git-svn-id: http://core.svn.wordpress.org/trunk@29279 1a063a9b-81f0-0310-95a4-ce76da25c4cd