Integrate map marking into static marking visitor.

Integrate map marking into static marking visitor.

This refactors the specialized marking of map contents to be done by the
static marking visitor shared between full and incremental marking. This
also fixes an issue where some maps weren't accounted for in the object
stats tracker. But more importantly, it simplifies the code base.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/10919294

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12526 ce2b1a6d-e550-0410-aec6-3dcde31c8c00