Add and use AsciiAlphaToLower.  Move RemoveLast test.  Add Clear test. This is a commit of http://codereview.chromium.org/3307003/show http://codereview.chromium.org/3312007/show and http://codereview.chromium.org/3341002/show for tfarina

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5409 ce2b1a6d-e550-0410-aec6-3dcde31c8c00