Reviewed by Darin Adler.

        HTML5 TreeBuilder regressed a Peacekeeper DOM test by 40%
        https://bugs.webkit.org/show_bug.cgi?id=48719

        It's unclear exactly what the Peacekeeper benchmark is testing,
        because I haven't found a way to run it myself.

        However, I constructed a benchmark which shows at least one possible slow point.
        The HTML5 spec talks about creating a new document for every time we use
        the fragment parsing algorithm.  Document() it turns out, it a huge bloated
        mess, and the constructor and destructor do a huge amount of work.
        To avoid constructing (or destructing) documents for each innerHTML call,
        this patch adds a shared dummy document used by all innerHTML calls.

        * benchmarks/parser/tiny-innerHTML.html: Added.
2011-01-28  Eric Seidel  <eric@webkit.org>

        Reviewed by Darin Adler.

        HTML5 TreeBuilder regressed a Peacekeeper DOM test by 40%
        https://bugs.webkit.org/show_bug.cgi?id=48719

        It's unclear exactly what the Peacekeeper benchmark is testing,
        because I haven't found a way to run it myself.

        However, I constructed a benchmark which shows at least one possible slow point.
        The HTML5 spec talks about creating a new document for every time we use
        the fragment parsing algorithm.  Document() it turns out, it a huge bloated
        mess, and the constructor and destructor do a huge amount of work.
        To avoid constructing (or destructing) documents for each innerHTML call,
        this patch adds a shared dummy document used by all innerHTML calls.

        This patch brings us from 7x slower than Safari 5 on tiny-innerHTML
        to only 1.5x slower than Safari 5.  I'm sure there is more work to do here.

        Saving a shared Document like this is error prone.  Currently
        DummyDocumentFactory::releaseDocument() calls removeAllChildren()
        in an attempt to clear the Document's state. However it's possible
        that that call is not sufficient and we'll have future bugs here.

        * html/parser/HTMLTreeBuilder.cpp:
        (WebCore::DummyDocumentFactory::createDummyDocument):
        (WebCore::DummyDocumentFactory::releaseDocument):
        (WebCore::HTMLTreeBuilder::FragmentParsingContext::FragmentParsingContext):
        (WebCore::HTMLTreeBuilder::FragmentParsingContext::document):
        (WebCore::HTMLTreeBuilder::FragmentParsingContext::finished):
        * html/parser/HTMLTreeBuilder.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@77050 268f45cc-cd09-0410-ab3c-d52691b4dbfc