Harmony: implement Math.trunc.

src/harmony-math.js

Index: src/harmony-math.js
diff --git a/src/harmony-math.js b/src/harmony-math.js
index 2e9b42a75e7cf368af023c29baaf9cd24663a3b8..a4d3f2e8a5e9c5936630571644605402dee1199d 100644
--- a/src/harmony-math.js
+++ b/src/harmony-math.js
@@ -29,7 +29,7 @@
 
 // ES6 draft 09-27-13, section 20.2.2.28.
 function MathSign(x) {
-  if (!IS_NUMBER(x)) x = NonNumberToNumber(x);
+  x = TO_NUMBER_INLINE(x);
   if (x > 0) return 1;
   if (x < 0) return -1;
   if (x === 0) return x;
@@ -37,12 +37,23 @@ function MathSign(x) {
 }
 
 
+// ES6 draft 09-27-13, section 20.2.2.34.
+function MathTrunc(x) {
+  x = TO_NUMBER_INLINE(x);
+  if (x > 0) return MathFloor(x);
+  if (x < 0) return MathCeil(x);
+  if (x === 0) return x;
+  return NAN;
+}
+
+
 function ExtendMath() {
   %CheckIsBootstrapping();
 
   // Set up the non-enumerable functions on the Math object.
   InstallFunctions($Math, DONT_ENUM, $Array(
-    "sign", MathSign
+    "sign", MathSign,
+    "trunc", MathTrunc
   ));
 }