perf-discovery: use `get_unique_pull_path`

This performance command now use the new API, unless the benchmarked Mercurial
is older.

Differential Revision: https://phab.mercurial-scm.org/D10423

contrib/perf.py

@@ -915,6 +915,12 b' def perfdiscovery(ui, repo, path, **opts'
     """benchmark discovery between local repo and the peer at given path"""
     repos = [repo, None]
     timer, fm = gettimer(ui, opts)
+
+    try:
+        from mercurial.utils.urlutil import get_unique_pull_path
+
+        path = get_unique_pull_path(b'perfdiscovery', repo, ui, path)[0]
+    except ImportError:
     path = ui.expandpath(path)
 
     def s():