Reduce number of writes to DependentCode array when inserting dependent IC.

BUG=305878
LOG=Y
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/339843004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21873 ce2b1a6d-e550-0410-aec6-3dcde31c8c00