LGTM My only concern with the ResponseRewritters, is that the cache store data after rewrite, so if the rewriters change the cache data would need to be cleared. This is not a new issue, it just something we might want to consider.
Currently the ImageRewriter get resize parameters, which are passed in using HttpResponse params. To make sure the cache store different items for different resize, there is specific code in AbstractHttpCache.createKey that handle the specific params. I think this might need a more generic code instead of handling only three params. http://codereview.appspot.com/1276042/show
