Make HCapturedObjects non-deletable for DCE.

R=jkummerow@chromium.org
BUG=v8:2987
TEST=mjsunit/regress/regress-2987

Review URL: https://codereview.chromium.org/64433002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17569 ce2b1a6d-e550-0410-aec6-3dcde31c8c00