fsck: add a performance test

Add a plain performance test for "fsck". This test will not be used to
/ referred to in any upcoming commit of mine in this series, but
having a simple test for fsck performance is valuable, so let's add it
while we're at it.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/perf/p1450-fsck.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+test_description='Test fsck performance'
+
+. ./perf-lib.sh
+
+test_perf_large_repo
+
+test_perf 'fsck' '
+	git fsck
+'
+
+test_done