Fix behavior themes in Google Chrome

When I used the ace element in Chrome the themes wouldn't behave well. Whenever I changed the theme or re-initialized the ace-element then all styles on the editor would disappear. This fixes that problem.

I didn't fix this problem myself, credits go to [nightwing](https://github.com/nightwing) who helped me [here](https://github.com/ajaxorg/ace-builds/issues/37)
I tried this fix in Atom Shell (Chromium) and I get an exception here if I don't initialise `this.styles`.