We already generate skia.h to include all public headers for Fiddle.
This just includes it with -Wunused-parameter turned on as an error.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4901
Change-Id: Ia55a901c09a3c9c9d6d35a43259431dba3532ed9
Reviewed-on: https://skia-review.googlesource.com/4901
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
