Reviewed by Darin, landed by ap.

        - fix http://bugzilla.opendarwin.org/show_bug.cgi?id=9547
          Resize corner does not track the mouse accurately

        Test: fast/css/resize-corner-tracking.html

        * page/FrameView.cpp:
        (WebCore::FrameView::handleMousePressEvent): Store the offset from the layer's
        resizing corner where dragging has started.
        (WebCore::FrameView::handleMouseMoveEvent): Pass the stored offset to the
        layer's resize method.
        * rendering/RenderLayer.cpp:
        (WebCore::RenderLayer::resize): Added an offset parameter, which is added to
        the mouse location.
        For objects that may have intrinsic margins applied to them,
        added code to lift the margins into the object's style in order to keep them
        constant.
        Changed to take the content size as the base size if the box-sizing property
        is content-box.
        (WebCore::RenderLayer::offsetFromResizeCorner): Added. Returns the offset of the
        given point from the corner that tracks the mouse when resizing.
        * rendering/RenderLayer.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@15014 268f45cc-cd09-0410-ab3c-d52691b4dbfc