Implement in-heap backing store for typed arrays.

This adds a fixed array sub-type that will represent a backing store for
typed arrays allocated with TypedArray(length) construtor.

R=mvstanton@chromium.org, verwaest@chromium.org

Review URL: https://codereview.chromium.org/101413006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18651 ce2b1a6d-e550-0410-aec6-3dcde31c8c00