Oilpan: move DOM string collection objects to the Oilpan heap.

Turn DOMTokenList, DOMStringList, DOMStringMap and their derived objects
into garbage collected objects.

R=haraken@chromium.org,ager@chromium.org,erik.corry@gmail.com
BUG=340522

Review URL: https://codereview.chromium.org/258143002

git-svn-id: svn://svn.chromium.org/blink/trunk@173652 bbb929c8-8fbe-4397-9dbb-9b2b20218538