perf: define formatter locally for Mercurial earlier than 2.2

Before this patch, using ui.formatter() prevents perf.py from
measuring performance with Mercurial earlier than 2.2 (or
ae5f92e154d3), because ui.formatter() isn't available in such
Mercurial, even though there are some code paths for Mercurial earlier
than 2.2 in perf.py.

For example, setting "_prereadsize" attribute in perfindex() and
perfnodelookup() is effective only with hg earlier than 1.8 (or
61c9bc3da402).

This patch defines formatter class locally, and use it instead of the
value returned by ui.formatter(), if perf.py is used with Mercurial
earlier than 2.2.

In this case, we don't need to think about -T/--template option for
formatter, because previous patch made -T/--template disabled for
perf.py with Mercurial earlier than 3.2 (or 7a7eed5176a4).

contrib/perf.py

@@ -138,8 +138,42 b' def gettimer(ui, opts=None):'
     # redirect all to stderr
     ui = ui.copy()
     ui.fout = ui.ferr
+
     # get a formatter
-    fm = ui.formatter('perf', opts)
+    uiformatter = getattr(ui, 'formatter', None)
+    if uiformatter:
+        fm = uiformatter('perf', opts)
+    else:
+        # for "historical portability":
+        # define formatter locally, because ui.formatter has been
+        # available since 2.2 (or ae5f92e154d3)
+        from mercurial import node
+        class defaultformatter(object):
+            """Minimized composition of baseformatter and plainformatter
+            """
+            def __init__(self, ui, topic, opts):
+                self._ui = ui
+                if ui.debugflag:
+                    self.hexfunc = node.hex
+                else:
+                    self.hexfunc = node.short
+            def __nonzero__(self):
+                return False
+            def startitem(self):
+                pass
+            def data(self, **data):
+                pass
+            def write(self, fields, deftext, *fielddata, **opts):
+                self._ui.write(deftext % fielddata, **opts)
+            def condwrite(self, cond, fields, deftext, *fielddata, **opts):
+                if cond:
+                    self._ui.write(deftext % fielddata, **opts)
+            def plain(self, text, **opts):
+                self._ui.write(text, **opts)
+            def end(self):
+                pass
+        fm = defaultformatter(ui, 'perf', opts)
+
     # stub function, runs code only once instead of in a loop
     # experimental config: perf.stub
     if ui.configbool("perf", "stub"):