Fix IfBuilder to use instruction factories. Add missing instruction factories.

This also makes the instruction constructors private and fixes
all uses of the public constructors to use the factory methods
instead.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/23654051

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16808 ce2b1a6d-e550-0410-aec6-3dcde31c8c00