Make font_service a shared service

It seems unlikely that there's any value in having an isolated instance
per profile. Make sure any running instance of the service is shared
by all users.

Bug: 862553
Change-Id: I56a3894925c15ff0c90e9e02512092754c34be26
Reviewed-on: https://chromium-review.googlesource.com/1133418Reviewed-by: Dominik Röttsches <drott@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574213}

components/services/font/manifest.json

@@ -6,6 +6,9 @@
     "service_manager:connector": {
       "provides": {
         "font_service": [ "font_service.mojom.FontService" ]
+      },
+      "requires": {
+        "service_manager": [ "service_manager:all_users" ]
       }
     }
   }