Fix generated dart bindings for view_provider.

Previously:
`NoSuchMethodError: method not found: 'view_token_mojom'`

There's probably a bug in the dart bindings generator that imports of
views.mojom aren't made available here.

BUG=
R=azani@chromium.org, jeffbrown@google.com, rudominer@chromium.org

Review URL: https://codereview.chromium.org/1834533002 .
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/ui/view_provider.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/ui/view_provider.mojom.dart
index 659ccff..dff6bfa 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/ui/view_provider.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/ui/view_provider.mojom.dart
@@ -9,6 +9,7 @@
 import 'package:mojo/mojo/bindings/types/service_describer.mojom.dart' as service_describer;
 import 'package:mojo/mojo/service_provider.mojom.dart' as service_provider_mojom;
 import 'package:mojo_services/mojo/ui/views.mojom.dart' as views_mojom;
+import 'package:mojo_services/mojo/ui/view_token.mojom.dart' as view_token_mojom;
 
 
 
diff --git a/mojo/services/ui/views/interfaces/view_provider.mojom b/mojo/services/ui/views/interfaces/view_provider.mojom
index 5fc6cf9..e473a26 100644
--- a/mojo/services/ui/views/interfaces/view_provider.mojom
+++ b/mojo/services/ui/views/interfaces/view_provider.mojom
@@ -7,6 +7,7 @@
 
 import "mojo/public/interfaces/application/service_provider.mojom";
 import "mojo/services/ui/views/interfaces/views.mojom";
+import "mojo/services/ui/views/interfaces/view_token.mojom";
 
 // Provides a View upon request.
 //