Added icons.

devtools/manifest.json

@@ -3,6 +3,12 @@
 	"name": "Three.js DevTools",
 	"version": "1.4",
 	"description": "Developer tools extension for Three.js",
+	"icons": {
+		"16": "icons/16.png",
+		"32": "icons/32.png",
+		"48": "icons/48.png",
+		"128": "icons/128.png"
+	},
 	"devtools_page": "index.html",
 	"background": {
 		"service_worker": "background.js",