tree 782a906b7c06097376416de46f146c7e7e87a9f2
parent 7535f419e235e224559ee2b4b62ee6bfddc01556
author mtklein <mtklein@chromium.org> 1471963089 -0700
committer Commit bot <commit-bot@chromium.org> 1471963089 -0700

GN: make libwebp an optional dependency

This will be handy for folks who don't have libwebp, like Fuchsia.

I convinced myself that this is done right by:
  - building in all three modes (default and explicitly set both ways);
  - looking at verbose Ninja logs to see the presence/lack of SK_HAS_WEBP_LIBRARY;
  - running dm -m Codec, which passes with libwebp and segfault without it.

If this is viable, I intend to make all third-party dependencies optional
and follow this pattern.  :skia should link and degrade gracefully without
any of //third_party.  It's okay for tools to have hard third-party
dependencies; we just need them to get past the `gn gen` stage without them.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2270693004

Review-Url: https://codereview.chromium.org/2270693004