Fix !defined(SK_XML) builds

Add guards for dependent code.

TBR=
Change-Id: I49c0c90a2defc6f39589721f95562e9e0f17db13
Reviewed-on: https://skia-review.googlesource.com/144610
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
4 files changed