Answers for "how to add an icon to your extension"

add icon chrome extension

"icons": { "16": "icon16.png",
           "48": "icon48.png",
          "128": "icon128.png" },

how to add extension logo of chrome

{
  "manifest_version": 2,
  "name": "Demo",
  "description": "This is demo.",
  "version": "1.0",
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "browser_action": {
    "default_popup": "popup.html"
  },
  "permissions": ["activeTab", "storage"]
}