- fix <rdar://problem/5193416> REGRESSION: Selection on large pages extremely slow

        * dom/Document.cpp: (WebCore::Document::removeMarkers): Added an early exit for the common
        case where there are no markers. Changed code to iterate over all the nodes in the range
        instead of using TextIterator, which is more efficient.
        
        * page/Frame.cpp: (WebCore::Frame::respondToChangedSelection): Added checks for editable,
        so we don't bother doing work related to spell checking and grammar checking when changing
        the selection in non-editable text. Also rearranged the code so we only compute the old
        word boundaries and sentence boundaries when actually needed, and don't do the sentence
        range checks unless grammar checking is enabled.

        * platform/TextBreakIteratorICU.cpp:
        (WebCore::setUpIterator): Don't take a locale parameter. Always pass in currentTextBreakLocaleID.
        (WebCore::characterBreakIterator): Removed local parameter.
        (WebCore::wordBreakIterator): Ditto.
        (WebCore::lineBreakIterator): Ditto.
        (WebCore::sentenceBreakIterator): Ditto.

        * platform/mac/TextBreakIteratorInternalICUMac.mm:
        (WebCore::getTextBreakLocale): Broke out the code to actually get the locale.
        (WebCore::currentTextBreakLocaleID): This function now handles only the caching and calls
        getTextBreakLocale to actually figure it out.

        * editing/visible_units.cpp: Added lots of FIXME comments, but no code change.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@21611 268f45cc-cd09-0410-ab3c-d52691b4dbfc