Oilpan: Support the HTML parser thread in oilpan

After r170314, the HTML parser thread allocates on-heap objects such as CSSValues. So this CL supports the HTML parser thread in oilpan. Also this CL marks the CSSValue hierarchy with ThreadAffinity=AnyThread because CSSValue can be allocated by both main thread and parser threads.

BUG=340522

Review URL: https://codereview.chromium.org/216203006

git-svn-id: svn://svn.chromium.org/blink/trunk@170564 bbb929c8-8fbe-4397-9dbb-9b2b20218538