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    New Flickr doesn't get fast scrolling but should · a1c75d03
    simon.fraser@apple.com authored
    https://bugs.webkit.org/show_bug.cgi?id=116514
    
    Source/WebCore:
    
    Reviewed by Darin Adler.
    
    RenderObject increments and decrements a counter of slow repaint objects on
    FrameView when it sees style changes related to background-attachment:fixed.
    However, it omitted to decrement the count when a renderer with a fixed background
    was destroyed.
    
    This caused Flickr to never fall into fast scrolling mode, since it toggled
    display:none on an element with a fixed background during loading, then removed
    the fixed background.
    
    Did some minor cleanup of #ENABLE(FAST_MOBILE_SCROLLING) crap.
    
    Tests: platform/mac-wk2/tiled-drawing/slow-scrolling-background-toggle.html
           platform/mac-wk2/tiled-drawing/slow-scrolling-hidden-background-toggle.html
           platform/mac-wk2/tiled-drawing/slow-scrolling.html
    
    * rendering/RenderObject.cpp:
    (WebCore::shouldRepaintFixedBackgroundsOnScroll):
    (WebCore::RenderObject::styleWillChange):
    (WebCore::RenderObject::willBeRemovedFromTree):
    
    LayoutTests:
    
    Reviewed by Darin Adler.
    
    slow-scrolling-hidden-background-toggle.html actually tests this patch. The other
    two tests were added because there appear to be no tests for basic internals.mainThreadScrollingReasons()
    functionality.
    
    * platform/mac-wk2/tiled-drawing/slow-scrolling-background-toggle-expected.txt: Added.
    * platform/mac-wk2/tiled-drawing/slow-scrolling-background-toggle.html: Added.
    * platform/mac-wk2/tiled-drawing/slow-scrolling-expected.txt: Added.
    * platform/mac-wk2/tiled-drawing/slow-scrolling-hidden-background-toggle-expected.txt: Added.
    * platform/mac-wk2/tiled-drawing/slow-scrolling-hidden-background-toggle.html: Added.
    * platform/mac-wk2/tiled-drawing/slow-scrolling.html: Added.
    
    git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150529 268f45cc-cd09-0410-ab3c-d52691b4dbfc
    a1c75d03