Added vector-based loadic hydrogen stubs. Not yet callable.

The next step is to integrate the use of vector[slot] into the IC
infrastructure so it can do the right thing for a vector-based ic.
Then these stubs can be installed. For now, they immediately bail out
to the miss handler.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/499343002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23405 ce2b1a6d-e550-0410-aec6-3dcde31c8c00