Issue #1240 - Part 1 - Define a new BigInt primitive type. Based on https://bugzilla.mozilla.org/show_bug.cgi?id=1366287 Part 1.0. However leaving out the --enable-bigint changes.

js/public/Conversions.h

@@ -120,7 +120,7 @@ ToBoolean(HandleValue v)
     if (v.isSymbol())
         return true;
 
-    /* The slow path handles strings and objects. */
+    /* The slow path handles strings, BigInts and objects. */
     return js::ToBooleanSlow(v);
 }