Preserve identity on wrap_jso hack. Has known failures

tools/dom/templates/html/dartium/html_dartium.darttemplate

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // DO NOT EDIT
 // Auto-generated dart:html library.
 
 /**
  * HTML elements and other resources for web-based applications that need to
  * interact with the browser and the DOM (Document Object Model).
@@ skipping 376 matching lines @@
 /**
  * Create Dart class that maps to the JS Type, add the JsObject as an expando
  * on the Dart class and return the created Dart class.
  */
 wrap_jso(jsObject) {
   try {
     if (jsObject is! js.JsObject) {
       // JS Interop converted the object to a Dart class e.g., Uint8ClampedList.
       return jsObject;
     }
+
+    // To preserve identity, if we already have a wrapper for this, return it.
+    var existing;
+    if (jsObject is! js.JsArray) {
+      var existing = jsObject['dartClass_instance'];
+      try {
+        if (unwrap_jso(existing) == jsObject) {
+          return existing;
+        }
+      } catch(e) {}
+    }
     // Try the most general type conversions on it.
     // TODO(alanknight): We may be able to do better. This maintains identity,
     // which is useful, but expensive. And if we nest something that only
     // this conversion handles, how does that work? e.g. a list of maps of elements.
     var converted = convertNativeToDart_SerializedScriptValue(jsObject);
     if (!identical(converted, jsObject)) {
       return converted;
     }
     var constructor = jsObject['constructor'];
     if (__interop_checks) {
       debug_or_assert("constructor != null", constructor != null);
     }
     var jsTypeName = constructor['name'];
     if (__interop_checks) {
       debug_or_assert("constructor != null && jsTypeName.length > 0", constructor != null && jsTypeName.length > 0);
     }
 
     var dartClass_instance;
     if (jsObject.hasProperty('dart_class')) {
       // Got a dart_class (it's a custom element) use it it's already set up.
       dartClass_instance = jsObject['dart_class'];
     } else {
       var func = getHtmlCreateFunction(jsTypeName);
       if (func != null) {
         dartClass_instance = func();
         dartClass_instance.blink_jsObject = jsObject;
+        jsObject['dartClass_instance'] = dartClass_instance;
       }
     }
     return dartClass_instance;
   } catch(e, stacktrace){
     if (__interop_checks) {
       if (e is DebugAssertException)
         window.console.log("${e.message}\n ${stacktrace}");
       else
         window.console.log("${stacktrace}");
     }
   }
 
   return null;
 }
 
+
 /**
  * Create Dart class that maps to the JS Type that is the JS type being
  * extended using JS interop createCallback (we need the base type of the
  * custom element) not the Dart created constructor.
  */
 wrap_jso_custom_element(jsObject) {
   try {
     if (jsObject is! js.JsObject) {
       // JS Interop converted the object to a Dart class e.g., Uint8ClampedList.
       return jsObject;
@@ skipping 94 matching lines @@
 class JsoNativeFieldWrapper extends NativeFieldWrapperClass2 {}
 
 unwrap_jso(dartClass_instance) => dartClass_instance;
 wrap_jso(jsObject) => jsObject;
 make_dart_rectangle(r) => r;
 convertDartToNative_Dictionary(Map dict) => dict;
 List convertDartToNative_StringArray(List<String> input) => input;
 convertDartToNative_List(List input) => input;
 
 $endif