Use a walking visitor to traverse JSObject structure. The purpose is to prepare for more complex context-dependent walks of the structure, needed for allocation site and pretenuring work. Different visitors can be created that annotate the object in various ways.

BUG=
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/25025002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17001 ce2b1a6d-e550-0410-aec6-3dcde31c8c00