Use mojo Shelf interfaces for both mash and classic ash.

chrome/app/mash/chrome_mash_content_browser_manifest_overlay.json

 // NOTE: This overlay is applied to content_browser_manifest.json on top of
 // src/chrome/browser/chrome_content_browser_manifest_overlay.json.
 //
 // The resulting manifest is output to
 // ${out}/Packages/chrome_mash_content_browser/manifest.json and is used as the
 // manifest for "service:content_browser" (i.e. the browser process) when Chrome
 // is run in a Mash environment.
 {
   "capabilities": {
     "required": {
-      "service:ash": {
-        "interfaces": [
-          "ash::mojom::ShelfController",
-          "ash::mojom::SystemTray",
-          "ash::mojom::WallpaperController"
-        ]
-      },
+      "service:ash": { "classes": [ "ash" ] },
       "service:accessibility_autoclick": {
         "interfaces": [ "ash::autoclick::mojom::AutoclickController" ]
       },
       "service:mash_session": { "classes": [ "app" ] }
     }
   }
 }