Persistent variants of the GC collection types.

R=haraken@chromium.org, wibling@chromium.org
BUG=

Review URL: https://codereview.chromium.org/150013006

git-svn-id: svn://svn.chromium.org/blink/trunk@166845 bbb929c8-8fbe-4397-9dbb-9b2b20218538