Simplify the LookupIterator

BUG=
R=ishell@chromium.org

Review URL: https://codereview.chromium.org/570293002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23975 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Use the regular start incremental marking strategy in the idle notification.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/568023002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23976 ce2b1a6d-e550-0410-aec6-3dcde31c8c00