Use mojo Shelf interfaces for both mash and classic ash.

chrome/browser/chrome_content_browser_manifest_overlay.json

 {
   "name": "service:content_browser",
   "display_name": "Chrome",
   "capabilities": {
     "provided": {
       "renderer": [
         "autofill::mojom::AutofillDriver",
         "autofill::mojom::PasswordManagerDriver",
         "extensions::StashService",
         "metrics::mojom::LeakDetector",
         "startup_metric_utils::mojom::StartupMetricHost",
         "translate::mojom::ContentTranslateDriver"
       ],
       "gpu": [
         "metrics::mojom::CallStackProfileCollector"
       ],
       "ash": [
+        "ash::mojom::ShelfController",
         "ash::mojom::SystemTray",
         "ash::mojom::SystemTrayClient"
       ],
       "mash:launchable": [
         "mash::mojom::Launchable"
       ]
     }
   }
 }