I havent yet found a way to view GWT designer mode. I have installed gwt sdk, gwt designer and window builder on eclipse 4.2. View my installation details: 
I Can open a java file using window builder but cant see the source and design tabs at the bottom: 
Somebody help me figure out how to access designer mode.
I havent yet found a way to view GWT designer mode. I have installed
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Turns out its a bug and i was able to access designer mode by clicking switching between to a different layout under Google > Web Toolkit > Designer preferences
Thanks for providing answers guys 🙂