Reviewed by Adam Treat.

        Do not render the full frame when there is some elements with fixed positioning
        https://bugs.webkit.org/show_bug.cgi?id=33150

        The frame view take into acount the list of fixed object when scrolling
        the view. If the number of object is lower than a certain threshold, the pixel
        are blitted, and the invalidated area updated.

        * page/FrameView.cpp:
        (WebCore::FrameView::FrameView):
        (WebCore::FrameView::useSlowRepaints):
        (WebCore::FrameView::useSlowRepaintsIfNotOverlapped):
        (WebCore::FrameView::addFixedObject):
        (WebCore::FrameView::removeFixedObject):
        (WebCore::FrameView::scrollContentsFastPath):
        * page/FrameView.h:
        * platform/ScrollView.cpp:
        (WebCore::ScrollView::scrollContents):
        (WebCore::ScrollView::scrollContentsFastPath):
        * platform/ScrollView.h:
        * rendering/RenderBlock.h:
        (WebCore::RenderBlock::positionedObjects):
        * rendering/RenderBox.cpp:
        (WebCore::RenderBox::styleWillChange):
        * rendering/RenderObject.cpp:
        (WebCore::RenderObject::styleWillChange):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@55890 268f45cc-cd09-0410-ab3c-d52691b4dbfc