simplify render benchmark code

by using report.MakeFromFile instead of NewFileConnector

app/benchmark_internal_test.go

@@ -5,9 +5,6 @@ import (
 	"net/http"
 	"net/url"
 	"testing"
-	"time"
-
-	"golang.org/x/net/context"
 
 	"github.com/weaveworks/scope/render"
 	"github.com/weaveworks/scope/report"
@@ -15,22 +12,9 @@ import (
 )
 
 var (
-	benchReportFile = flag.String("bench-report-file", "", "json report file to use for benchmarking (relative to this package)")
+	benchReportFile = flag.String("bench-report-file", "", "report file to use for benchmarking (relative to this package)")
 )
 
-func loadReport() (report.Report, error) {
-	if *benchReportFile == "" {
-		return fixture.Report, nil
-	}
-
-	c, err := NewFileCollector(*benchReportFile, 0)
-	if err != nil {
-		return fixture.Report, err
-	}
-
-	return c.Report(context.Background(), time.Now())
-}
-
 func BenchmarkTopologyList(b *testing.B) {
 	benchmarkRender(b, func(report report.Report) {
 		request := &http.Request{
@@ -41,17 +25,22 @@ func BenchmarkTopologyList(b *testing.B) {
 }
 
 func benchmarkRender(b *testing.B, f func(report.Report)) {
-	report, err := loadReport()
-	if err != nil {
-		b.Fatal(err)
+	r := fixture.Report
+	if *benchReportFile != "" {
+		var err error
+		if r, err = report.MakeFromFile(*benchReportFile); err != nil {
+			b.Fatal(err)
+		}
 	}
+
 	b.ReportAllocs()
 	b.ResetTimer()
+
 	for i := 0; i < b.N; i++ {
 		b.StopTimer()
 		render.ResetCache()
 		b.StartTimer()
-		f(report)
+		f(r)
 	}
 }