Oilpan: have HTMLImport::recalcTreeState() use on-heap local variables.

R=wibling@chromium.org,haraken@chromium.org
BUG=357163

Review URL: https://codereview.chromium.org/394463003

git-svn-id: svn://svn.chromium.org/blink/trunk@178078 bbb929c8-8fbe-4397-9dbb-9b2b20218538