Fallback to unsupported browser type instead of returning null

Source/bindings/dart/DartDOMWrapper.cpp

 // Copyright 2011, Google Inc.
 // 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
@@ skipping 56 matching lines @@
         if (Dart_IsError(type)) {
             DartUtilities::reportProblem(domData->scriptExecutionContext(), type);
             break;
         }
 
         if (Dart_IsNull(type)) {
             searchid = DartWebkitClassInfo[searchid].base_class_id;
         }
     }
     if ((searchid <= 0) || Dart_IsError(type) || !Dart_IsType(type) || Dart_IsNull(type)) {
-        DartUtilities::reportProblem(domData->scriptExecutionContext(), type);
-        return Dart_Null();
+        Dart_Handle error;
+        if (Dart_IsError(type)) {
+            error = type;
+        } else {
+            char message[256];
+            snprintf(message, 256, "Unsupported native browser type: %s", DartWebkitClassInfo[cid].jsName);
+            error = Dart_NewApiError(message);
+        }
+        DartUtilities::reportProblem(domData->scriptExecutionContext(), error);
+        type = Dart_GetType(htmlLibrary, Dart_NewStringFromCString("_UnsupportedBrowserObject"), 0, 0);
     }
 
     persistentType = Dart_NewPersistentHandle(type);
     (*table)[cid] = persistentType;
 
     return persistentType;
 }
 
 Dart_Handle DartDOMWrapper::exceptionCodeToDartException(ExceptionCode exceptionCode, const String& message, DartDOMData* domData)
 {
@@ skipping 17 matching lines @@
 
 Dart_Handle DartDOMWrapper::exceptionCodeToDartException(DartExceptionState& exceptionState)
 {
     DartDOMData* domData = DartDOMData::current();
     DartApiScope dartApiScope;
 
     return exceptionCodeToDartException(exceptionState.code(), exceptionState.processedMessage(), domData);
 }
 
 }