Serendipitously arrange the tags so that String.length() becomes a branch-free

Serendipitously arrange the tags so that String.length() becomes a branch-free
operation.  I have another version of this change that does not remove the
special inline caches for difference sized strings.  The other version is ever
so slightly faster, but the nice thing about this version is that it removes
253 lines of code.
Review URL: http://codereview.chromium.org/8187

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@603 ce2b1a6d-e550-0410-aec6-3dcde31c8c00