Bindings generation emits (more) correct null checking

Source/bindings/dart/custom/DartMessageEventCustom.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 105 matching lines @@
             goto fail;
 
         DartStringAdapter originArg = DartUtilities::dartToString(args, 5, exception);
         if (exception)
             goto fail;
 
         DartStringAdapter lastEventIdArg = DartUtilities::dartToString(args, 6, exception);
         if (exception)
             goto fail;
 
-        LocalDOMWindow* sourceArg = DartWindow::toNative(Dart_GetNativeArgument(args, 7), exception);
+        LocalDOMWindow* sourceArg = DartWindow::toNativeWithNullCheck(Dart_GetNativeArgument(args, 7), exception);
         if (exception)
             goto fail;
 
         OwnPtr<MessagePortArray> portArray;
         if (!Dart_IsNull(Dart_GetNativeArgument(args, 8))) {
             portArray = adoptPtr(new MessagePortArray);
             ArrayBufferArray bufferArray;
             DartUtilities::toMessagePortArray(Dart_GetNativeArgument(args, 8), *portArray, bufferArray, exception);
             if (exception)
                 goto fail;
             if (bufferArray.size() > 0) {
                 exception = Dart_NewStringFromCString("MessagePortArray argument must contain only MessagePorts");
                 goto fail;
             }
         }
 
         receiver->initMessageEvent(typeArg, canBubbleArg, cancelableArg, dataArg, originArg, lastEventIdArg, sourceArg, portArray.release());
         return;
     }
 
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
 
 }
 
 }