Remove infrastructure for experimental JS natives

src/debug/mirrors.js

Index: src/debug/mirrors.js
diff --git a/src/debug/mirrors.js b/src/debug/mirrors.js
index b534fecdc41bb4e741dd374802e61e58a931318a..8096f2c54e00607c6dc7697bb6902e297ad86c7b 100644
--- a/src/debug/mirrors.js
+++ b/src/debug/mirrors.js
@@ -11,17 +11,10 @@
 var GlobalArray = global.Array;
 var IsNaN = global.isNaN;
 var JSONStringify = global.JSON.stringify;
-var MapEntries;
-var MapIteratorNext;
-var SetIteratorNext;
-var SetValues;
-
-utils.Import(function(from) {
-  MapEntries = from.MapEntries;
-  MapIteratorNext = from.MapIteratorNext;
-  SetIteratorNext = from.SetIteratorNext;
-  SetValues = from.SetValues;
-});
+var MapEntries = global.Map.prototype.entries;
+var MapIteratorNext = (new global.Map).entries().next;
+var SetIteratorNext = (new global.Set).values().next;
+var SetValues = global.Set.prototype.values;
 
 // ----------------------------------------------------------------------------