Make incremental marker post-process JSWeakCollection.

R=hpayer@chromium.org
BUG=v8:2070
LOG=N

Review URL: https://codereview.chromium.org/301553003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21552 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Repairs to FLAG_pretenure_call_new.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/307583002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21553 ce2b1a6d-e550-0410-aec6-3dcde31c8c00