Rename WebCrypto::digest2 --> WebCrypto::digest

(part of a three-sided patch)

BUG=245025
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/19384009

git-svn-id: svn://svn.chromium.org/blink/trunk@154581 bbb929c8-8fbe-4397-9dbb-9b2b20218538