narrow: add progress-reporting when looking for local changes in `hg tracked`

Looking for local changes (changes not on the given remote) can take a
long time, so we should have progress-reporting for it.

Differential Revision: https://phab.mercurial-scm.org/D10501

hgext/narrow/narrowcommands.py

@@ -227,8 +227,15 b' def _narrow('
     unfi = repo.unfiltered()
     outgoing = discovery.findcommonoutgoing(unfi, remote, commoninc=commoninc)
     ui.status(_(b'looking for local changes to affected paths\n'))
+    progress = ui.makeprogress(
+        topic=_(b'changesets'),
+        unit=_(b'changesets'),
+        total=len(outgoing.missing) + len(outgoing.excluded),
+    )
     localnodes = []
+    with progress:
     for n in itertools.chain(outgoing.missing, outgoing.excluded):
+            progress.increment()
         if any(oldmatch(f) and not newmatch(f) for f in unfi[n].files()):
             localnodes.append(n)
     revstostrip = unfi.revs(b'descendants(%ln)', localnodes)