Use mojo SystemTray interfaces for both mash and classic ash

chrome/app/mojo/chrome_manifest.json

 {
   "manifest_version": 1,
   "name": "exe:chrome",
   "display_name": "Chrome",
   "capabilities": {
     "required": {
       "*": { "classes": [ "app", "mash:launchable" ] },
       "mojo:ash": {
         "interfaces": [
           "ash::mojom::ShelfController",
           "ash::mojom::SystemTray",
           "ash::mojom::WallpaperController"
         ]
       },
       "mojo:accessibility_autoclick": {
          "interfaces": [ "ash::autoclick::mojom::AutoclickController" ]
       }
     },
-    "provided": { "mash:launchable": [ "mash::mojom::Launchable" ] }
+    "provided": {
+      "mash:launchable": [
+        "mash::mojom::Launchable"
+      ],
+      "ash": [
+        "ash::mojom::SystemTrayClient"
+      ]
+    }
   }
 }