Reviewed by Darin.
        
        On Mac, support fine grained wheel events generated by trackpad and Mighty Mouse.
        http://bugs.webkit.org/show_bug.cgi?id=13134
        <rdar://problem/5076249?

        * WebCore.exp:
            Export _wkGetWheelEventDeltas
        * page/EventHandler.cpp:
        (WebCore::EventHandler::handleWheelEvent):
            Remove (0, 0) scroll event hack, it is not needed anymore.
            Do per-pixel scrolling for fine grained events.
        * platform/PlatformWheelEvent.h:
        (WebCore::PlatformWheelEvent::isContinuous):
            Add new m_isContinuous boolean to indicate fine grained wheel events.
        * platform/ScrollBar.cpp:
        (WebCore::Scrollbar::Scrollbar):
        (WebCore::Scrollbar::setValue):
        (WebCore::Scrollbar::setSteps):
        (WebCore::Scrollbar::scroll):
        * platform/ScrollBar.h:
        (WebCore::Scrollbar::value):
            Use float to represent current position to support finer grained scrolling.
            Add ScrollByPixel, remove ScrollByWheel (which was same as ScrollByLine anyway)
        * platform/ScrollTypes.h:
        (WebCore::):
        * platform/gdk/WheelEventGdk.cpp:
        (WebCore::PlatformWheelEvent::PlatformWheelEvent):
            Initalize m_isContinuous
        * platform/mac/WebCoreSystemInterface.h:
        * platform/mac/WebCoreSystemInterface.mm:
            Add wkGetWheelEventDeltas for getting fine grained wheel events
        * platform/mac/WheelEventMac.mm:
        (WebCore::PlatformWheelEvent::PlatformWheelEvent):
            Get the wheel deltas using new wkGetWheelEventDeltas interface
        * platform/qt/WheelEventQt.cpp:
        (WebCore::PlatformWheelEvent::PlatformWheelEvent):
            Initalize m_isContinuous
        * rendering/RenderListBox.cpp:
        (WebCore::RenderListBox::calcHeight):
            Pass item height to scrollbar

WebKit:

        Reviewed by Darin.
        
        On Mac, support fine grained wheel events generated by trackpad and Mighty Mouse.
        http://bugs.webkit.org/show_bug.cgi?id=13134
        <rdar://problem/5076249?

        * WebCoreSupport/WebSystemInterface.m:
        (InitWebCoreSystemInterface): Expose GetWheelEventDeltas()

WebKitLibraries:

        Reviewed by Darin.
        
        Added wkGetWheelEventDeltas

        * WebKitSystemInterface.h:
        * libWebKitSystemInterface.a:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@20506 268f45cc-cd09-0410-ab3c-d52691b4dbfc