Fallback to unsupported browser type instead of returning null

Source/bindings/dart/DartDOMWrapper.cpp

Index: Source/bindings/dart/DartDOMWrapper.cpp
diff --git a/Source/bindings/dart/DartDOMWrapper.cpp b/Source/bindings/dart/DartDOMWrapper.cpp
index f73b9091e9978daef8fb4beadf3daee02d5e4c5e..70a6b843be95ec3b6ff570d8c116832b02b06d4f 100644
--- a/Source/bindings/dart/DartDOMWrapper.cpp
+++ b/Source/bindings/dart/DartDOMWrapper.cpp
@@ -74,8 +74,16 @@ Dart_PersistentHandle DartDOMWrapper::dartClass(
         }
     }
     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);