accounting: change stats interface

This is done to make clear ownership over accounting object and prepare
for removing global stats object.

Stats elapsed time calculation has been altered to account for actual
transfer time instead of stats creation time.

fs/operations/multithread_test.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"testing"
 
+	"github.com/ncw/rclone/fs/accounting"
+
 	"github.com/ncw/rclone/fs"
 	"github.com/ncw/rclone/fstest"
 	"github.com/stretchr/testify/assert"
@@ -49,6 +51,7 @@ func TestMultithreadCopy(t *testing.T) {
 		{size: multithreadChunkSize*2 + 1, streams: 2},
 	} {
 		t.Run(fmt.Sprintf("%+v", test), func(t *testing.T) {
+			var err error
 			contents := fstest.RandomString(test.size)
 			t1 := fstest.Time("2001-02-03T04:05:06.499999999Z")
 			file1 := r.WriteObject(context.Background(), "file1", contents, t1)
@@ -57,8 +60,13 @@ func TestMultithreadCopy(t *testing.T) {
 
 			src, err := r.Fremote.NewObject(context.Background(), "file1")
 			require.NoError(t, err)
+			accounting.Stats.ResetCounters()
+			tr := accounting.Stats.NewTransfer(src)
 
-			dst, err := multiThreadCopy(context.Background(), r.Flocal, "file1", src, 2)
+			defer func() {
+				tr.Done(err)
+			}()
+			dst, err := multiThreadCopy(context.Background(), r.Flocal, "file1", src, 2, tr)
 			require.NoError(t, err)
 			assert.Equal(t, src.Size(), dst.Size())
 			assert.Equal(t, "file1", dst.Remote())