Make function proxies work as constructors.

src/v8natives.js

Index: src/v8natives.js
diff --git a/src/v8natives.js b/src/v8natives.js
index 10cd4affbba9b19e0d6a1e90d3c0ae360caaaa40..13a3e9ed379d3064831342a68a2383d21e6d2561 100644
--- a/src/v8natives.js
+++ b/src/v8natives.js
@@ -1045,13 +1045,21 @@ function ProxyFix(obj) {
   if (IS_UNDEFINED(props)) {
     throw MakeTypeError("handler_returned_undefined", [handler, "fix"]);
   }
-
   if (IS_FUNCTION(obj)) {
     var callTrap = %GetCallTrap(obj);
     var constructTrap = %GetConstructTrap(obj);
     var code = DelegateCallAndConstruct(callTrap, constructTrap);
     %Fix(obj);  // becomes a regular function
     %SetCode(obj, code);
+    // TODO(rossberg): What about length and other properties? Not specified.
+    // We just put in some half-reasonable defaults for now.
+    var prototype = new $Object();
+    $Object.defineProperty(prototype, "constructor",
+      {value: obj, writable: true, enumerable: false, configrable: true});
+    $Object.defineProperty(obj, "prototype",
+      {value: prototype, writable: true, enumerable: false, configrable: false})
+    $Object.defineProperty(obj, "length",
+      {value: 0, writable: true, enumerable: false, configrable: false});
   } else {
     %Fix(obj);
   }