Maintain referential integrity of proxy instances in dart:js

sdk/lib/js/dartium/js_dartium.dart

Index: sdk/lib/js/dartium/js_dartium.dart
diff --git a/sdk/lib/js/dartium/js_dartium.dart b/sdk/lib/js/dartium/js_dartium.dart
index a0c48ea0d93ed32372e0262d46effebb8c054aef..2ad4bf3e5f02fd5d2f2f579a17a82f6e68bc9895 100644
--- a/sdk/lib/js/dartium/js_dartium.dart
+++ b/sdk/lib/js/dartium/js_dartium.dart
@@ -242,7 +242,8 @@ abstract class Serializable<T> {
   T toJs();
 }
 
-// A table to managed local Dart objects that are proxied in JavaScript.
+// A table to managed local Dart objects that are proxied in JavaScript,
+// or proxies to JavaScript objects.
 class _ProxiedObjectTable {
   // Debugging name.
   final String _name;
@@ -283,9 +284,9 @@ class _ProxiedObjectTable {
   }
 
   // Adds a new object to the table and return a new ID for it.
-  String add(x) {
+  String add(x, {String id}) {
     // TODO(vsm): Cache x and reuse id.
-    final id = '$_name-${_nextId++}';
+    id = (id != null) ? id : '$_name-${_nextId++}';
     _registry[id] = x;
     return id;
   }
@@ -347,8 +348,13 @@ _deserialize(var message) {
       // Local function.
       return _proxiedObjectTable.get(id);
     } else {
-      // Remote function.  Forward to its port.
-      return new JsFunction._internal(port, id);
+      // Remote function.
+      var jsFunction = _proxiedObjectTable.get(id);
+      if (jsFunction == null) {
+        jsFunction = new JsFunction._internal(port, id);
+        _proxiedObjectTable.add(jsFunction, id: id);
+      }
+      return jsFunction;
     }
   }
 
@@ -360,7 +366,12 @@ _deserialize(var message) {
       return _proxiedObjectTable.get(id);
     } else {
       // Remote object.
-      return new JsObject._internal(port, id);
+      var jsObject = _proxiedObjectTable.get(id);
+      if (jsObject == null) {
+        jsObject = new JsObject._internal(port, id);
+        _proxiedObjectTable.add(jsObject, id: id);
+      }
+      return jsObject;
     }
   }