Make fuzzers use cleaner interface

Make fuzzers use cleaner interface

signalBoring() no longer exists.  When the fuzzer runs out of randomness,
it just returns 0.  Fuzzers should not go into infinite loops if this
happens.  do while loops are particularly error-prone.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3963

Change-Id: Iebcfc14cc6b0a19c5dd015cd39875c81fa44003e
Reviewed-on: https://skia-review.googlesource.com/3963
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>