This reduces the binary size by making the Is* type-test functions non-virtual.

I had to change Gap and Label instructions to have a common abstract superclass because both act as gap-instructions for the register allocator.
Review URL: http://codereview.chromium.org/6880204

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7691 ce2b1a6d-e550-0410-aec6-3dcde31c8c00