Fix bug introduced by r13960.

Fix bug introduced by r13960.

Allocator does not backtrack thus during allocation we must not create an unhandled live
range which starts before the start of the current live range.

If such range is added to the list of unhandled it might see an inconsistent state of active/inactive live-ranges as they are retired to handled as soon as start of the current live range is larger than their end.

Add assertion to catch this kind of bugs early.

TEST=NavierStokes does not fail on ARM

Review URL: https://codereview.chromium.org/14262005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14274 ce2b1a6d-e550-0410-aec6-3dcde31c8c00