Remove margin collapsing.

sky/engine/core/rendering/RenderBox.h

Index: sky/engine/core/rendering/RenderBox.h
diff --git a/sky/engine/core/rendering/RenderBox.h b/sky/engine/core/rendering/RenderBox.h
index 44393f422e03d414883d8075d8e3d2b14bdd2f80..270fce6dd53d36bd6584e21f792a7c838b2fb041 100644
--- a/sky/engine/core/rendering/RenderBox.h
+++ b/sky/engine/core/rendering/RenderBox.h
@@ -303,17 +303,6 @@ public:
         m_marginBox.setEnd(styleToUse->direction(), value);
     }
 
-    // The following five functions are used to implement collapsing margins.
-    // All objects know their maximal positive and negative margins.  The
-    // formula for computing a collapsed margin is |maxPosMargin| - |maxNegmargin|.
-    // For a non-collapsing box, such as a leaf element, this formula will simply return
-    // the margin of the element.  Blocks override the maxMarginBefore and maxMarginAfter
-    // methods.
-    enum MarginSign { PositiveMargin, NegativeMargin };
-    virtual bool isSelfCollapsingBlock() const { return false; }
-    virtual LayoutUnit collapsedMarginBefore() const { return marginBefore(); }
-    virtual LayoutUnit collapsedMarginAfter() const { return marginAfter(); }
-
     virtual void absoluteRects(Vector<IntRect>&, const LayoutPoint& accumulatedOffset) const override;
     virtual void absoluteQuads(Vector<FloatQuad>&) const override;