This adds:
* A script (tools/update-wasm-fuzzers.sh), which creates a new fuzzing seed
  corpus and uploads to google storage (you must have the right credentials).
* A new pair of DEPS entries to pull in the current version of the corpus
  based on a checked in pair of hash files.

BUG=None
TEST=None
R=ahaas@chromium.org,kcc@chromium.org,mvstanton@chromium.org

Review-Url: https://codereview.chromium.org/2273303002
Cr-Commit-Position: refs/heads/master@{#38987}