Oilpan: add NeedsAdjustAndMark<T> unit test.

Basic test coverage for the NeedsAdjustAndMark<T> template.

R=haraken@chromium.org
BUG=

Review URL: https://codereview.chromium.org/293543003

git-svn-id: svn://svn.chromium.org/blink/trunk@174258 bbb929c8-8fbe-4397-9dbb-9b2b20218538