all: remove use of deprecated NewMessage

Replace NewMessage calls with NewField, NewElement, or NewValue.

Change-Id: I6d2bb4f11f0eb2ba7a52308b1addb111137ad4b9
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/193266
Reviewed-by: Joe Tsai <joetsai@google.com>
diff --git a/encoding/bench_test.go b/encoding/bench_test.go
index 3b64aab..d5ae728 100644
--- a/encoding/bench_test.go
+++ b/encoding/bench_test.go
@@ -61,9 +61,9 @@
 func setScalarField(m pref.Message, fd pref.FieldDescriptor, level int) {
 	switch fd.Kind() {
 	case pref.MessageKind, pref.GroupKind:
-		m2 := m.NewMessage(fd)
-		fillMessage(m2, level+1)
-		m.Set(fd, pref.ValueOf(m2))
+		val := m.NewField(fd)
+		fillMessage(val.Message(), level+1)
+		m.Set(fd, val)
 	default:
 		m.Set(fd, scalarField(fd.Kind()))
 	}
@@ -109,9 +109,9 @@
 	switch fd.Kind() {
 	case pref.MessageKind, pref.GroupKind:
 		for i := 0; i < 10; i++ {
-			m := list.NewMessage()
-			fillMessage(m, level+1)
-			list.Append(pref.ValueOf(m))
+			val := list.NewElement()
+			fillMessage(val.Message(), level+1)
+			list.Append(val)
 		}
 	default:
 		for i := 0; i < 100; i++ {
@@ -128,9 +128,9 @@
 	pkey := scalarField(keyDesc.Kind())
 	switch kind := valDesc.Kind(); kind {
 	case pref.MessageKind, pref.GroupKind:
-		m := mmap.NewMessage()
-		fillMessage(m, level+1)
-		mmap.Set(pkey.MapKey(), pref.ValueOf(m))
+		val := mmap.NewValue()
+		fillMessage(val.Message(), level+1)
+		mmap.Set(pkey.MapKey(), val)
 	default:
 		mmap.Set(pkey.MapKey(), scalarField(kind))
 	}