Implement the `Math.TAU` constant.

src/harmony-math.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 'use strict';
 
 // ES6 draft 09-27-13, section 20.2.2.28.
 function MathSign(x) {
   x = TO_NUMBER_INLINE(x);
   if (x > 0) return 1;
@@ skipping 203 matching lines @@
            x * (1/5 - x * (1/6 - x * (1/7)))))));
   } else {  // Use regular log if not close enough to 0.
     return MathLog(1 + x);
   }
 }
 
 
 function ExtendMath() {
   %CheckIsBootstrapping();
 
+  // Set up math constants.
+  InstallConstants($Math, $Array(
+    "TAU", 6.283185307179586
+  ));
+
   // Set up the non-enumerable functions on the Math object.
   InstallFunctions($Math, DONT_ENUM, $Array(
     "sign", MathSign,
     "trunc", MathTrunc,
     "sinh", MathSinh,
     "cosh", MathCosh,
     "tanh", MathTanh,
     "asinh", MathAsinh,
     "acosh", MathAcosh,
     "atanh", MathAtanh,
     "log10", MathLog10,
     "log2", MathLog2,
     "hypot", MathHypot,
     "fround", MathFroundJS,
     "clz32", MathClz32,
     "cbrt", MathCbrt,
     "log1p", MathLog1p,
     "expm1", MathExpm1
   ));
 }
 
 
 ExtendMath();