Simplify heap profile disposal logic

Profile removal is initiated by ProfileType which dispatches notifications to all clients.

BUG=None
R=alph@chromium.org

Review URL: https://codereview.chromium.org/139853010

git-svn-id: svn://svn.chromium.org/blink/trunk@165641 bbb929c8-8fbe-4397-9dbb-9b2b20218538