Set wallpaper from right click menu in Files app.

ui/file_manager/file_manager/manifest.json

 {
   // chrome-extension://hhaomjibdihmijegdhdafkllkbggdgoj/
   "key": "MIGdMA0GCSqGSIb3DQEBAQUAA4GLADCBhwKBgQDlhpGghtnNJ7pluQN0RDwbUxwwi99oM35ZEaFYvxPLrf0fIEC18cfDdJi6u4aJ+UoSpgzK731L0P/k4LvK2Rz9kVKOy0+IvuRrWkT7lbrLfA1UEBh02OA1AAshjmyRg4IxCqgl8ia8XWq6HKegS1y1KXZYGgb4qp7Bh9VC4cIzswIBIw==",
   "manifest_version": 2,
   "name": "Files",
   "version": "3.0",
   "description": "File Manager",
   "incognito" : "split",
   "icons": {
     "16": "common/images/icon16.png",
@@ skipping 26 matching lines @@
     "https://www.google-analytics.com/",
     "launcherSearchProvider",
     "mediaGalleries",
     "mediaPlayerPrivate",
     "metricsPrivate",
     "notifications",
     "power",
     "storage",
     "syncFileSystem",
     "unlimitedStorage",
+    "wallpaper",
     "webstoreWidgetPrivate",
     "webview"
   ],
   "file_browser_handlers": [
     {
       "id": "mount-archive",
       "default_title": "__MSG_MOUNT_ARCHIVE__",
       "default_icon": "common/images/file_types/200/archive.png",
       "file_filters": [
         "filesystem:*.rar",
@@ skipping 160 matching lines @@
         "background/js/test_util_base.js",
         "background/js/test_util.js",
         "background/js/volume_manager.js",
         "background/js/background.js"
       ]
     },
     // chrome-extension://pmfjbimdmchhbnneeidfognadeopoehp is the image loader extension.
     "content_security_policy": "default-src 'none'; script-src 'self' blob: filesystem: chrome://resources chrome-extension://pmfjbimdmchhbnneeidfognadeopoehp chrome-extension://fbjakikfhfdajcamjleinfciajelkpek; style-src 'self' blob: filesystem: 'unsafe-inline' chrome://resources chrome-extension://fbjakikfhfdajcamjleinfciajelkpek; frame-src 'self' blob: filesystem: about:; img-src 'self' blob: filesystem: chrome://resources chrome://theme data: https://docs.google.com https://*.googleusercontent.com chrome://extension-icon; media-src 'self' blob: filesystem: https://*.googleusercontent.com; connect-src https://drive.google.com https://www.google-analytics.com chrome://resources; object-src 'self' blob: filesystem:; font-src chrome://resources;"
   }
 }