Remove functionality only used by the memory purger, which is now gone.

BUG=350455
TEST=none
R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/199363003

git-svn-id: svn://svn.chromium.org/blink/trunk@169150 bbb929c8-8fbe-4397-9dbb-9b2b20218538