Build fails when MediaDesciption.h is included in a file with no other dependencies which already require the AtomicString header.
Created attachment 290498 [details] Patch
Comment on attachment 290498 [details] Patch Actually, does <wtf/Forward.h> work?
Created attachment 290585 [details] Patch
Yes, Forward.h works at the expense of having to include the AtomicString header in the final cpp file. It seems a good compromise.
Comment on attachment 290585 [details] Patch For this you wouldn't even need to upload the patch for review. It could be an unreviewed build fix.
And it is something you can land now, no need to wait for other MSE changes.
Comment on attachment 290585 [details] Patch Clearing flags on attachment: 290585 Committed r206952: <http://trac.webkit.org/changeset/206952>
All reviewed patches have been landed. Closing bug.