More information about the compilation levels of closure are available here:
In cocos2d-html5 the jscomp task is being used which has a little more information here:
Generally closure always "minifies". It is the degree of minification.
The default is simple and it does do some variable replacement. The lightest treatment would probably be to do whitespace only and do a pretty print (you can get it to do this in Chrome as well in the debug tool).
So your comp task might look like
<jscomp compilationLevel="whitespace" prettyprint="true" warning="quiet" debug="false" output="../lib/Cocos2d-html5-v2.2.2.min.js">
Doing so would be good for debugging but terrible for performance and download size (you should be using advanced for that which is not in the build.xml by default but I can confirm that cocos works just fine if you go to that level of compilation.