Sync our homegrown SysInfo replacement with the one in Chrome base.

Also fix several inconsistencies/bugs on the way.

TEST=base-unittests
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/510693003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23435 ce2b1a6d-e550-0410-aec6-3dcde31c8c00