Reviewed by Darin

    Reviewed by Darin

        Move subrange helper function from spellchecking code to TextIterator

        * editing/TextIterator.h:
        added TextIterator::subrange
        * editing/TextIterator.cpp:
        (WebCore::CharacterIterator::advance):
        early return if count is <= 0; assert that it's not < 0
        (WebCore::TextIterator::subrange):
        new function, moved from FrameMac.mmm

        * bridge/mac/FrameMac.mm:
        moved subrange() function to TextIterator
        (WebCore::FrameMac::advanceToNextMisspelling):
        use TextIterator::subrange
        (WebCore::markAllMisspellingsInRange):
        ditto
        (WebCore::markAllBadGrammarInRange):
        ditto

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@17980 268f45cc-cd09-0410-ab3c-d52691b4dbfc