Pass in the prototype to CreateApiFunction rather than setting it on the result.

src/apinatives.js

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 53 matching lines @@
 
 function InstantiateFunction(data, name) {
   // We need a reference to kApiFunctionCache in the stack frame
   // if we need to bail out from a stack overflow.
   var cache = kApiFunctionCache;
   var serialNumber = %GetTemplateField(data, kApiSerialNumberOffset);
   var isFunctionCached =
    (serialNumber in cache) && (cache[serialNumber] != kUninitialized);
   if (!isFunctionCached) {
     try {
-      var fun = %CreateApiFunction(data);
-      if (name) %FunctionSetName(fun, name);
       var flags = %GetTemplateField(data, kApiFlagOffset);
-      var doNotCache = flags & (1 << kDoNotCacheBit);
-      if (!doNotCache) cache[serialNumber] = fun;
-      if (flags & (1 << kRemovePrototypeBit)) {
-        %FunctionRemovePrototype(fun);
-      } else {
-        var prototype = %GetTemplateField(data, kApiPrototypeTemplateOffset);
-        // Note: Do not directly use an object template as a condition, our
-        // internal ToBoolean doesn't handle that!
-        fun.prototype = typeof prototype === 'undefined' ?
-            {} : Instantiate(prototype);
-        if (flags & (1 << kReadOnlyPrototypeBit)) {
-          %FunctionSetReadOnlyPrototype(fun);
-        }
-        %SetProperty(fun.prototype, "constructor", fun, DONT_ENUM);
+      var has_proto = !(flags & (1 << kRemovePrototypeBit));
+      var prototype;
+      if (has_proto) {
+        var template = %GetTemplateField(data, kApiPrototypeTemplateOffset);
+        prototype = typeof template === 'undefined'
+            ?  {} : Instantiate(template);
+
         var parent = %GetTemplateField(data, kApiParentTemplateOffset);
         // Note: Do not directly use a function template as a condition, our
         // internal ToBoolean doesn't handle that!
-        if (!(typeof parent === 'undefined')) {
+        if (typeof parent !== 'undefined') {
           var parent_fun = Instantiate(parent);
-          %SetPrototype(fun.prototype, parent_fun.prototype);
+          %SetPrototype(prototype, parent_fun.prototype);
         }
       }
+      var fun = %CreateApiFunction(data, prototype);
+      if (name) %FunctionSetName(fun, name);
+      var doNotCache = flags & (1 << kDoNotCacheBit);
+      if (!doNotCache) cache[serialNumber] = fun;
+      if (has_proto && flags & (1 << kReadOnlyPrototypeBit)) {
+        %FunctionSetReadOnlyPrototype(fun);
+      }
       ConfigureTemplateInstance(fun, data);
       if (doNotCache) return fun;
     } catch (e) {
       cache[serialNumber] = kUninitialized;
       throw e;
     }
   }
   return cache[serialNumber];
 }
 
@@ skipping 22 matching lines @@
             obj, name, getter, setter, attribute, access_control);
       } else {
         throw "Bad properties array";
       }
       i += length + 1;
     }
   } finally {
     if (requires_access_checks) %EnableAccessChecks(obj);
   }
 }