Use the right kind of guard for debug code.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/232883002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20665 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Avoid type assertion on object comparison in Hydrogen - the comparison is unreachable because of previous checks.

BUG=
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/232053004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20666 ce2b1a6d-e550-0410-aec6-3dcde31c8c00