Move all RefPtr's to CSSValue to oilpan transition types, except for the one in CSSCursorImageValue.

This change gets rid of all but one RefPtr to CSSValue. I have introduced a few persistents core/animation/..., core/css/StylePropertySet, and ElementStyleResources. I plan to attack the one in CSSCursorImageValue subsequently, and then change CSSValue from RefCountedGarbageCollected to GarbageCollectedFinalized.

R=ager@chromium.org, erik.corry@gmail.com, haraken@chromium.org, oilpan-reviews@chromium.org, tkent@chromium.org, vegorov@chromium.org, zerny@chromium.org
BUG=341815
NOTRY=true

Review URL: https://codereview.chromium.org/184313004

git-svn-id: svn://svn.chromium.org/blink/trunk@168466 bbb929c8-8fbe-4397-9dbb-9b2b20218538