In <http://trac.webkit.org/r169407>, the RenderView pointer argument was removed from RenderStyle::getRoundedBorderFor(), but the code in computeRoundedRectForBoxShape() was never updated to remove the pointers.

Newer versions of clang now warn about taking the address of a reference value (and the fact that it will never be NULL):

Source/WebCore/rendering/shapes/BoxShape.cpp:74:117: error: reference cannot be bound to dereferenced null pointer in well-defined C++ code; pointer may be assumed to always convert to true [-Werror,-Wundefined-bool-conversion]
        RoundedRect::Radii radii = computeMarginBoxShapeRadii(style.getRoundedBorderFor(renderer.borderBoxRect(), &(renderer.view())).radii(), renderer);
                                                              ~~~~~                                                ~^~~~~~~~~~~~~~~~
In file included from Source/WebCore/rendering/shapes/BoxShape.cpp:33:
In file included from Source/WebCore/rendering/RenderBox.h:26:
In file included from Source/WebCore/rendering/RenderBoxModelObject.h:28:
In file included from Source/WebCore/rendering/RenderLayerModelObject.h:26:
In file included from Source/WebCore/rendering/RenderElement.h:27:
Source/WebCore/rendering/RenderObject.h:571:17: note: 'view' returns a reference
    RenderView& view() const { return *document().renderView(); };
                ^
Source/WebCore/rendering/shapes/BoxShape.cpp:90:70: error: reference cannot be bound to dereferenced null pointer in well-defined C++ code; pointer may be assumed to always convert to true [-Werror,-Wundefined-bool-conversion]
        return style.getRoundedBorderFor(renderer.borderBoxRect(), &(renderer.view()));
               ~~~~~                                                ~^~~~~~~~~~~~~~~~
In file included from Source/WebCore/rendering/shapes/BoxShape.cpp:33:
In file included from Source/WebCore/rendering/RenderBox.h:26:
In file included from Source/WebCore/rendering/RenderBoxModelObject.h:28:
In file included from Source/WebCore/rendering/RenderLayerModelObject.h:26:
In file included from Source/WebCore/rendering/RenderElement.h:27:
Source/WebCore/rendering/RenderObject.h:571:17: note: 'view' returns a reference
    RenderView& view() const { return *document().renderView(); };
                ^
Source/WebCore/rendering/shapes/BoxShape.cpp:94:66: error: reference cannot be bound to dereferenced null pointer in well-defined C++ code; pointer may be assumed to always convert to true [-Werror,-Wundefined-bool-conversion]
    return style.getRoundedBorderFor(renderer.borderBoxRect(), &(renderer.view()));
           ~~~~~                                                ~^~~~~~~~~~~~~~~~
In file included from Source/WebCore/rendering/shapes/BoxShape.cpp:33:
In file included from Source/WebCore/rendering/RenderBox.h:26:
In file included from Source/WebCore/rendering/RenderBoxModelObject.h:28:
In file included from Source/WebCore/rendering/RenderLayerModelObject.h:26:
In file included from Source/WebCore/rendering/RenderElement.h:27:
Source/WebCore/rendering/RenderObject.h:571:17: note: 'view' returns a reference
    RenderView& view() const { return *document().renderView(); };
                ^
3 errors generated.