Move the Location class into the AST Expression class as a member.

Move the Location class into the AST Expression class as a member.
Since it is (currently) only an enum, change it to an enum (for now).

Review URL: http://codereview.chromium.org/342035

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3181 ce2b1a6d-e550-0410-aec6-3dcde31c8c00