SkWebpCodec: enable a loop count of 1

Commit 557fbb added animation support to SkWebpCodec, with the intent to
match Chromium. This was during the ~1.5 year period between
crbug.com/592735 and crbug.com/649264 when Chromium attempted to align
WebP with GIF, and play the animation once more than the stored number
(see crbug.com/592735). This was later reverted, because it means that a
WebP is unable to play an animation a single time (see
crbug.com/649264). This commit catches SkWebpCodec up with Chromium.

Add a legacy build flag (SK_LEGACY_WEBP_LOOP_COUNT) so we can stage the
change on Android.

Change-Id: If07e00d5e070847ceeb9ce27cd78a846974cdb4d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/259161
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
2 files changed