Add constant twoPiDouble/twoPiFloat to MathExtras.h

Source/core/svg/SVGPathParser.cpp

Index: Source/core/svg/SVGPathParser.cpp
diff --git a/Source/core/svg/SVGPathParser.cpp b/Source/core/svg/SVGPathParser.cpp
index 6b7ac433993d717552ee32e63c1de09094de4f5e..57ba8a5164b2010d4690f425db17bd605ed147a6 100644
--- a/Source/core/svg/SVGPathParser.cpp
+++ b/Source/core/svg/SVGPathParser.cpp
@@ -456,9 +456,9 @@ bool SVGPathParser::decomposeArcToCubic(float angle, float rx, float ry, FloatPo
 
     float thetaArc = theta2 - theta1;
     if (thetaArc < 0 && sweepFlag)
-        thetaArc += 2 * piFloat;
+        thetaArc += twoPiFloat;
     else if (thetaArc > 0 && !sweepFlag)
-        thetaArc -= 2 * piFloat;
+        thetaArc -= twoPiFloat;
 
     pointTransform.makeIdentity();
     pointTransform.rotate(angle);