RegExpMacroAssembler::CheckStackGuardState should update input string pointer when it is moved or changed by GC.

If input string was cons-string it might undergo short-circuiting during GC. This does not change input start if underlying seq-string (first element of cons-string) does not move but this makes input-string pointer on the native regexp's frame invalid.

R=lrn@chromium.org

Review URL: http://codereview.chromium.org/8343001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9697 ce2b1a6d-e550-0410-aec6-3dcde31c8c00