playground/socket: fix message buffering

Use time.After to avoid the finnicky antics of
correctly resetting a time.Timer.

Fixes golang/go#13749

Change-Id: I3f1ed17a31d981996e2bb7a8155c3ba0ec723c7d
Reviewed-on: https://go-review.googlesource.com/19942
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

playground/socket/socket.go

@@ -264,7 +264,6 @@ func buffer(in <-chan *Message) <-chan *Message {
 	go func() {
 		defer close(out)
 		var (
-			t     = time.NewTimer(msgDelay)
 			tc    <-chan time.Time
 			buf   []byte
 			kind  string
@@ -293,8 +292,7 @@ func buffer(in <-chan *Message) <-chan *Message {
 					flush()
 					kind = m.Kind
 					if tc == nil {
-						tc = t.C
-						t.Reset(msgDelay)
+						tc = time.After(msgDelay)
 					}
 				}
 				buf = append(buf, m.Body...)