Web Animations API: Remove caching in camelCaseCSSPropertyNameToID to prevent crash.

BUG=328532

Review URL: https://codereview.chromium.org/119053002

git-svn-id: svn://svn.chromium.org/blink/trunk@164207 bbb929c8-8fbe-4397-9dbb-9b2b20218538