Use requestAnimationFrame (without prefix) in calendar picker

This is a prerequisite for deprecating the prefixed function, because
otherwise the forms tests get a deprecation message. This internal use
of webkitRequestAnimationFrame may also have inflated the use counter
data for it.

BUG=354921
R=abarth@chromium.org, keishi@chromium.org, tkent@chromium.org

Review URL: https://codereview.chromium.org/209003012

git-svn-id: svn://svn.chromium.org/blink/trunk@169918 bbb929c8-8fbe-4397-9dbb-9b2b20218538