Oilpan: Fix lsan integration to properly balance register/unregister calls.

R=earthdok@chromium.org, haraken@chromium.org, tkent@chromium.org
BUG=378404

Review URL: https://codereview.chromium.org/316573002

git-svn-id: svn://svn.chromium.org/blink/trunk@175396 bbb929c8-8fbe-4397-9dbb-9b2b20218538