Don't add change listeners to pixelRefs in DDL mode

Change-Id: I1ddfec1e0d697dd4ed183c304514b14c89aca11d
Reviewed-on: https://skia-review.googlesource.com/115400
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
3 files changed