Change [Pass]RefPtr's of simpler CSS value subclasses to oilpan transition types.

To allow for making small changes wrt. our oilpan transition I have added support in PassRefPtr and RefPtr for converting from a RawPtr to PassRefPtr/RefPtr. It should be safe since ref'ing an extra time will never be a correctness issue.

R=ager@chromium.org, erik.corry@gmail.com, haraken@chromium.org, vegorov@chromium.org, zerny@chromium.org
BUG=341815

Review URL: https://codereview.chromium.org/152323006

git-svn-id: svn://svn.chromium.org/blink/trunk@166781 bbb929c8-8fbe-4397-9dbb-9b2b20218538