[builtins] Refactor the remaining Date builtins.

src/js/json.js

Index: src/js/json.js
diff --git a/src/js/json.js b/src/js/json.js
index ee3b9dceea217062f077131c5807b3716352a6e5..b8836eaddd919fb9387c962391f4075e7df8e302 100644
--- a/src/js/json.js
+++ b/src/js/json.js
@@ -11,6 +11,7 @@
 // -------------------------------------------------------------------
 // Imports
 
+var GlobalDate = global.Date;
 var GlobalJSON = global.JSON;
 var GlobalSet = global.Set;
 var InternalArray = utils.InternalArray;
@@ -247,6 +248,24 @@ utils.InstallFunctions(GlobalJSON, DONT_ENUM, [
 ]);
 
 // -------------------------------------------------------------------
+// Date.toJSON
+
+// 20.3.4.37 Date.prototype.toJSON ( key )
+function DateToJSON(key) {
+  var o = TO_OBJECT(this);
+  var tv = TO_PRIMITIVE_NUMBER(o);
+  if (IS_NUMBER(tv) && !NUMBER_IS_FINITE(tv)) {
+    return null;
+  }
+  return o.toISOString();
+}
+
+// Set up non-enumerable functions of the Date prototype object.
+utils.InstallFunctions(GlobalDate.prototype, DONT_ENUM, [
+  "toJSON", DateToJSON
+]);
+
+// -------------------------------------------------------------------
 // JSON Builtins
 
 function JsonSerializeAdapter(key, object) {