make big-endian very opt-in

Change-Id: I578d064660cb20b834b80898ddc18e2f36394f11
Reviewed-on: https://skia-review.googlesource.com/c/167685
Reviewed-by: Hal Canary <halcanary@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed