Add constant twoPiDouble/twoPiFloat to MathExtras.h

Source/wtf/MathExtras.h

Index: Source/wtf/MathExtras.h
diff --git a/Source/wtf/MathExtras.h b/Source/wtf/MathExtras.h
index 1b97859b4bf60691f79079063a77b43be55cccff..c4945061e8d2f732a22e99cb69b4b6ce88faf839 100644
--- a/Source/wtf/MathExtras.h
+++ b/Source/wtf/MathExtras.h
@@ -49,6 +49,9 @@ const float piOverTwoFloat = static_cast<float>(M_PI_2);
 const double piOverFourDouble = M_PI_4;
 const float piOverFourFloat = static_cast<float>(M_PI_4);
 
+const double twoPiDouble = piDouble * 2.0;
+const float twoPiFloat = piFloat * 2.0f;
+
 #if OS(MACOSX)
 
 // Work around a bug in the Mac OS X libc where ceil(-0.1) return +0.