Reviewed by Alexey
        
        Test that this works correctly with composed characters
        http://bugs.webkit.org/show_bug.cgi?id=12833
        REGRESSION: Selecting text in 6.6MB txt file is sluggish as of the Feb 19th nightly
        <rdar://problem/5028159>

        * fast/text/large-text-composed-char-expected.checksum: Added.
        * fast/text/large-text-composed-char-expected.png: Added.
        * fast/text/large-text-composed-char-expected.txt: Added.
        * fast/text/large-text-composed-char.html: Added.

WebCore:

        Reviewed by Alexey.

        Fix http://bugs.webkit.org/show_bug.cgi?id=12833
        REGRESSION: Selecting text in 6.6MB txt file is sluggish as of the Feb 19th nightly
        <rdar://problem/5028159>
        
        Divide large text blocks (>64kB) over multiple text nodes. This limits linebox searches to
        a manageable subset.
        
        * dom/Text.cpp:
        (WebCore::Text::createWithLengthLimit):
        * dom/Text.h:
        * html/HTMLParser.cpp:
        (WebCore::HTMLParser::parseToken):
        * loader/TextDocument.cpp:
        (WebCore::TextTokenizer::write):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@20127 268f45cc-cd09-0410-ab3c-d52691b4dbfc