Maintain referential integrity of proxy instances in dart:js

pkg/browser/lib/interop.js

Index: pkg/browser/lib/interop.js
diff --git a/pkg/browser/lib/interop.js b/pkg/browser/lib/interop.js
index 8577e4f28b8c30aa67270ff78727da5789d0bea0..fd475597ab7139891b959ccfcffff10ffb8a5d06 100644
--- a/pkg/browser/lib/interop.js
+++ b/pkg/browser/lib/interop.js
@@ -14,7 +14,7 @@ function ReceivePortSync() {
 }
 
 // Type for remote proxies to Dart objects with dart2js.
-function DartProxy(o) {
+function DartObject(o) {
   this.o = o;
 }
 
@@ -250,16 +250,16 @@ function DartProxy(o) {
     return Object.keys(this.map).length;
   }
 
+  var _dartRefPropertyName = "_$dart_ref";
+
   // Adds an object to the table and return an ID for serialization.
   ProxiedObjectTable.prototype.add = function (obj) {
-    for (var ref in this.map) {
-      var o = this.map[ref];
-      if (o === obj) {
-        return ref;
-      }
+    var ref = obj[_dartRefPropertyName];
+    if (ref == null) {
+      ref = this.name + '-' + this._nextId++;
+      this.map[ref] = obj;
+      Object.defineProperty(obj, _dartRefPropertyName, { value: ref });
     }
-    var ref = this.name + '-' + this._nextId++;
-    this.map[ref] = obj;
     return ref;
   }
 
@@ -328,7 +328,7 @@ function DartProxy(o) {
   proxiedObjectTable._initialize()
 
   // Type for remote proxies to Dart objects.
-  function DartProxy(id, sendPort) {
+  function DartObject(id, sendPort) {
     this.id = id;
     this.port = sendPort;
   }
@@ -361,7 +361,7 @@ function DartProxy(o) {
                  proxiedObjectTable.add(message),
                  proxiedObjectTable.sendPort ];
       }
-    } else if (message instanceof DartProxy) {
+    } else if (message instanceof DartObject) {
       // Remote object proxy.
       return [ 'objref', message.id, message.port ];
     } else {
@@ -417,7 +417,7 @@ function DartProxy(o) {
     }
   }
 
-  // Creates a DartProxy to forwards to the remote object.
+  // Creates a DartObject to forwards to the remote object.
   function deserializeObject(message) {
     var id = message[1];
     var port = message[2];
@@ -427,7 +427,7 @@ function DartProxy(o) {
       return proxiedObjectTable.get(id);
     } else {
       // Remote object.
-      return new DartProxy(id, port);
+      return new DartObject(id, port);
     }
   }