encoding/xml: remove unnecessary memory allocation in Unmarshal

benchmark              old ns/op     new ns/op     delta
BenchmarkUnmarshal     75256         72626         -3.49%

benchmark              old allocs     new allocs     delta
BenchmarkUnmarshal     259            219            -15.44%

Change-Id: I7fd30739b045e35b95e6ef6a8ef2f15b0dd6839c
Reviewed-on: https://go-review.googlesource.com/2758
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/encoding/xml/marshal_test.go b/src/encoding/xml/marshal_test.go
index 14f73a7..cdd52ff 100644
--- a/src/encoding/xml/marshal_test.go
+++ b/src/encoding/xml/marshal_test.go
@@ -1148,12 +1148,14 @@
 }
 
 func BenchmarkMarshal(b *testing.B) {
+	b.ReportAllocs()
 	for i := 0; i < b.N; i++ {
 		Marshal(atomValue)
 	}
 }
 
 func BenchmarkUnmarshal(b *testing.B) {
+	b.ReportAllocs()
 	xml := []byte(atomXml)
 	for i := 0; i < b.N; i++ {
 		Unmarshal(xml, &Feed{})