mash: Move directly linked NewWindowDelegate to mojom::NewWindowClient.

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.
 {
   "interface_provider_specs": {
     "service_manager:connector": {
       "provides": {
         "content_browser:ash": [
+          "ash::mojom::NewWindowClient",
           "ash::mojom::SystemTrayClient",
           "ash::mojom::VolumeController",
           "ash::mojom::WallpaperManager",
           "app_list::mojom::AppListPresenter",
           "keyboard::mojom::Keyboard"
         ]
       },
       "requires": {
         "service:ash": [ "ash" ],
         "service:accessibility_autoclick": [ "ash:autoclick" ],
-        "service:mash_session": [ "app" ]
+        "service:mash_session": [ "app" ],
+        "service:task_viewer": [ "mash:launchable" ]
       }
     }
   }
 }