Serializer enable/disable flags need thread safety.

BUG=
R=hpayer@chromium.org, svenpanne@chromium.org

Review URL: https://codereview.chromium.org/240193002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20855 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Make Heap::AllocateRaw*String private.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/241023002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20856 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Merge remote-tracking branch 'upstream/bleeding_edge' into bleeding_edge