mountinfo: add benchmark for unescape

    go test -v -test.benchmem -count=10 -run ^$ -bench BenchmarkUnescape .
    go: downloading golang.org/x/sys v0.1.0
    goos: linux
    goarch: arm64
    pkg: github.com/moby/sys/mountinfo
    BenchmarkUnescape
    BenchmarkUnescape-10     1000000      1068 ns/op     640 B/op      31 allocs/op
    BenchmarkUnescape-10      992292      1082 ns/op     640 B/op      31 allocs/op
    BenchmarkUnescape-10     1000000      1050 ns/op     640 B/op      31 allocs/op
    BenchmarkUnescape-10     1000000      1038 ns/op     640 B/op      31 allocs/op
    BenchmarkUnescape-10     1000000      1034 ns/op     640 B/op      31 allocs/op
    BenchmarkUnescape-10     1000000      1045 ns/op     640 B/op      31 allocs/op
    BenchmarkUnescape-10     1000000      1071 ns/op     640 B/op      31 allocs/op
    BenchmarkUnescape-10     1000000      1033 ns/op     640 B/op      31 allocs/op
    BenchmarkUnescape-10     1000000      1032 ns/op     640 B/op      31 allocs/op
    BenchmarkUnescape-10     1000000      1070 ns/op     640 B/op      31 allocs/op
    PASS
    ok  github.com/moby/sys/mountinfo 10.653s

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

mountinfo/mountinfo_linux_test.go

@@ -771,3 +771,32 @@ func TestUnescape(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkUnescape(b *testing.B) {
+	testCases := []string{
+		"",
+		"/",
+		"/some/longer/path",
+		"/path\\040with\\040spaces",
+		"/path/with\\134backslash",
+		"/tab\\011in/path",
+		`/path/"with'quotes`,
+		`/path/"with'quotes,\040space,\011tab`,
+		`\12`,
+		`\134`,
+		`"'"'"'`,
+		`/\1345`,
+		`/\12x`,
+		`\0`,
+		`\x`,
+		"\\\\",
+	}
+
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		for x := 0; x < len(testCases); x++ {
+			_, _ = unescape(testCases[x])
+		}
+	}
+}