Use mojo volume interfaces for 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": {
     "provided": {
       "content_browser:ash": [
         "ash::mojom::SystemTrayClient",
+        "ash::mojom::VolumeController",
         "ash::mojom::WallpaperManager",
         "app_list::mojom::AppListPresenter",
         "keyboard::mojom::Keyboard"
       ]
     },
     "required": {
       "service:ash": [ "ash" ],
       "service:accessibility_autoclick": [ "ash:autoclick" ],
       "service:mash_session": [ "app" ]
     }
   }
 }