This simple refactoring makes it very clear that clearing non-live transitions
actually consists of 2 quite separate things. Things would even be nicer if the
prototype transitions were represented by a separate data structure instead of
reusing FixedArray in an interesting way once again.

As an additional bonus, this CL makes it possible to read each of the methods in
question on a 30" screen without scrolling!

Review URL: https://chromiumcodereview.appspot.com/9169045

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10501 ce2b1a6d-e550-0410-aec6-3dcde31c8c00