tracing: add a couple of trace points on obsolete and repoview

I was seeing weird stalls in some fast commands, and these trace
events help explain them.

Differential Revision: https://phab.mercurial-scm.org/D6550

mercurial/obsolete.py

@@ -899,6 +899,7 b' def getrevs(repo, name):'
 
     Such access may compute the set and cache it for future use"""
     repo = repo.unfiltered()
+    with util.timedcm('getrevs %s', name):
     if not repo.obsstore:
         return frozenset()
     if name not in repo.obsstore.caches:

mercurial/repoview.py

@@ -274,7 +274,7 b' class repoview(object):'
         unfiindex = unfichangelog.index
         unfilen = len(unfiindex)
         unfinode = unfiindex[unfilen - 1][7]
-
+        with util.timedcm('repo filter for %s', self.filtername):
         revs = filterrevs(unfi, self.filtername, self._visibilityexceptions)
         cl = self._clcache
         newkey = (unfilen, unfinode, hash(revs), unfichangelog._delayed)