It may be useful to look at Chrome plugin code at times for debugging purpose. Chrome plugins are stored in the following directory (for user user1) on Mac:
"/Users/user1/Library/Application Support/Google/Chrome/Default/Extensions/"
Each plugin has a directory of its own (e.g. gplegfbjlmmehdoakndmohflojccocli). To find directory for a specific plugin (say PageSpeed) one can look for that name in all manifest.json files. Here is the handy command for that:
$ find ~/Library/Application\ Support/Google/Chrome/Default/Extensions -name "manifest.json" -exec grep -H -i "PageSpee" {} \; | grep name
/Users/user1/Library/Application Support/Google/Chrome/Default/Extensions/gplegfbjlmmehdoakndmohflojccocli/2.0.4.3_0/manifest.json: "name": "PageSpeed Insights (by Google)",
