Rework BoxBorderPainter's mitre clipping logic

Source/core/paint/BoxBorderPainter.h

Index: Source/core/paint/BoxBorderPainter.h
diff --git a/Source/core/paint/BoxBorderPainter.h b/Source/core/paint/BoxBorderPainter.h
index 9586e07ea48fdd3daa396f4b3c048f375601dc37..b167b46fd482984dbf3236e5bcd280f9be468845 100644
--- a/Source/core/paint/BoxBorderPainter.h
+++ b/Source/core/paint/BoxBorderPainter.h
@@ -28,6 +28,11 @@ public:
 
 private:
     struct ComplexBorderInfo;
+    enum MitreType {

[fs, 2015/06/08 21:06:31]

Maybe MiterType (etc.) so them Americans understand too ;-)

+        NoMitre,
+        SoftMitre, // Anti-aliased
+        HardMitre, // Not anti-aliased
+    };
 
     BorderEdgeFlags paintOpacityGroup(GraphicsContext*, const ComplexBorderInfo&, unsigned index,
         float accumulatedOpacity) const;
@@ -39,10 +44,12 @@ private:
 
     void drawBoxSideFromPath(GraphicsContext*, const LayoutRect&, const Path&, float thickness,
         float drawThickness, BoxSide, Color, EBorderStyle) const;
-    void clipBorderSidePolygon(GraphicsContext*, BoxSide, bool firstEdgeMatches,
-        bool secondEdgeMatches) const;
+    void clipBorderSidePolygon(GraphicsContext*, BoxSide, MitreType mitre1, MitreType mitre2) const;
     void clipBorderSideForComplexInnerPath(GraphicsContext*, BoxSide) const;
 
+    MitreType computeMitre(BoxSide, BoxSide adjacentSide, BorderEdgeFlags, bool antialias) const;
+    static bool mitresRequireClipping(MitreType mitre1, MitreType mitre2, EBorderStyle, bool antialias);
+
     const BorderEdge& firstEdge() const
     {
         ASSERT(m_visibleEdgeSet);