In order to implement bug 209240, we need a way in WebCore to mark a rejected promise as handled.
<rdar://problem/60592359>
Created attachment 393886 [details] Patch
Created attachment 393887 [details] Patch
Created attachment 393889 [details] Patch
Comment on attachment 393889 [details] Patch r=me
Committed r258664: <https://trac.webkit.org/changeset/258664>