Using the "source" icon [=] is weird, especially since all other breakpoint types have an icon. I'd imagine that it would be something like a [U] (for URL) or [C] (for containing) and [M] (for matching).
Created attachment 373575 [details] Patch
Created attachment 373576 [details] [Image] After Patch is applied
Created attachment 373669 [details] Patch Extend the "tails" of the arrows to the edge of the box.
Created attachment 373671 [details] [Image] After Patch is applied
Comment on attachment 373669 [details] Patch Looks good! r=me
Comment on attachment 373669 [details] Patch Clearing flags on attachment: 373669 Committed r247237: <https://trac.webkit.org/changeset/247237>
All reviewed patches have been landed. Closing bug.
<rdar://problem/52804997>