Move Mus into chrome's process when running with --mus.

chrome/app/BUILD.gn

Index: chrome/app/BUILD.gn
diff --git a/chrome/app/BUILD.gn b/chrome/app/BUILD.gn
index 5797be91c731d94efde914ef84303cc7d89491d1..71fc9b9d1c809bc51052cf32cf256030c30d2402 100644
--- a/chrome/app/BUILD.gn
+++ b/chrome/app/BUILD.gn
@@ -408,7 +408,10 @@ service_manifest("chrome_content_packaged_services_manifest_overlay") {
       "//chrome/browser/chrome_content_packaged_services_manifest_overlay.json"
   packaged_services = chrome_packaged_services
   if (is_chromeos) {
-    packaged_services += [ "//ash/mus:manifest" ]
+    packaged_services += [
+      "//ash/mus:manifest",
+      "//services/ui:manifest",
+    ]
   }
 }