Prepare push to trunk.  Now working on version 3.24.6.

R=jkummerow@chromium.org
BUG=

Review URL: https://codereview.chromium.org/98643011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18371 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Use concurrent sweeping instead of parallel sweeping by default.

LOG=n
R=hpayer@chromium.org, mstarzinger@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/100433006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18374 ce2b1a6d-e550-0410-aec6-3dcde31c8c00