[CSS Shapes] Empty polygons with non-zero shape-padding cause an ASSERT crash

Source/core/rendering/shapes/PolygonShape.cpp

 /*
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
  *    disclaimer.
@@ skipping 164 matching lines @@
             appendArc(*marginVertices, thisEdge.vertex1(), margin, prevOffsetEdge.vertex2(), thisOffsetEdge.vertex1(), false);
     }
 
     snapVerticesToLayoutUnitGrid(*marginVertices);
     return adoptPtr(new FloatPolygon(marginVertices.release(), fillRule));
 }
 
 const FloatPolygon& PolygonShape::shapePaddingBounds() const
 {
     ASSERT(shapePadding() >= 0);
-    if (!shapePadding())
+    if (!shapePadding() || m_polygon.isEmpty())
         return m_polygon;
 
     if (!m_paddingBounds)
         m_paddingBounds = computeShapePaddingBounds(m_polygon, shapePadding(), m_polygon.fillRule());
 
     return *m_paddingBounds;
 }
 
 const FloatPolygon& PolygonShape::shapeMarginBounds() const
 {
     ASSERT(shapeMargin() >= 0);
-    if (!shapeMargin())
+    if (!shapeMargin() || m_polygon.isEmpty())
         return m_polygon;
 
     if (!m_marginBounds)
         m_marginBounds = computeShapeMarginBounds(m_polygon, shapeMargin(), m_polygon.fillRule());
 
     return *m_marginBounds;
 }
 
 static inline bool getVertexIntersectionVertices(const EdgeIntersection& intersection, FloatPoint& prevVertex, FloatPoint& thisVertex, FloatPoint& nextVertex)
 {
@@ skipping 314 matching lines @@
             }
         }
     }
 
     if (firstFitFound)
         result = LayoutUnit::fromFloatCeil(firstFitRect.y());
     return firstFitFound;
 }
 
 } // namespace WebCore