UIContextMenuInteraction implementation for WKContentView
<rdar://problem/51875189>
Created attachment 372414 [details] Patch
Created attachment 372415 [details] Patch
Created attachment 372417 [details] Patch
Created attachment 372419 [details] Patch
Comment on attachment 372419 [details] Patch rs=me once EWS is green.
Created attachment 372444 [details] Patch
Created attachment 372446 [details] Patch
Committed r246583: <https://trac.webkit.org/changeset/246583>