Rename shell namespace to service_manager

chrome/app/mash/chrome_mash_manifest.json

 {
   // NOTE: This is the manifest for service:chrome_mash, which is only used to
   // package services for the Mash environment when baked into the Chrome binary
   // (i.e. "chrome --mash")
   //
   // If you need to require or provide capabilities from Chrome itself within
   // the Mash environment, you should instead modify
   // chrome_mash_content_browser_manifest_overlay.json.
   "manifest_version": 1,
   "name": "service:chrome_mash",
   "display_name": "Chrome Mash Packaged Services",
   "capabilities": {
     "provided": {
-      "shell:service_factory": [ "shell::mojom::ServiceFactory" ]
+      "shell:service_factory": [ "service_manager::mojom::ServiceFactory" ]
     },
     "required": {
       "service:mash_session": [ "app" ],
       "service:catalog": [ "control" ]
     }
   }
 }