Enable parallel sweeping.

BUG=

Review URL: https://codereview.chromium.org/12255002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13650 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix verify heap problem when parallel sweeping is enabled.

BUG=

Review URL: https://codereview.chromium.org/12260004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13651 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Reduces memory consumption for parallel sweeping.

BUG=

Review URL: https://codereview.chromium.org/12177011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13652 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Limit stack size of sweeper threads.

BUG=

Review URL: https://codereview.chromium.org/12256006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13653 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: Add separate flag for --trace-stub-failures

Port r13598 (79a374cf)

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/12211088

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13654 ce2b1a6d-e550-0410-aec6-3dcde31c8c00