Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo_services/lib/mojo/url_response_disk_cache.mojom.dart

Index: mojo/dart/packages/mojo_services/lib/mojo/url_response_disk_cache.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/url_response_disk_cache.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/url_response_disk_cache.mojom.dart
index 5f76f4f93d4c55ea2007a09424be42379933a8d6..3a12e8cfd484b392d955f7cf8c99ab752bdb2699 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/url_response_disk_cache.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/url_response_disk_cache.mojom.dart
@@ -669,11 +669,14 @@ const int _UrlResponseDiskCache_updateAndGetExtractedName = 4;
 
 
 class _UrlResponseDiskCacheServiceDescription implements service_describer.ServiceDescription {
-  dynamic getTopLevelInterface([Function responseFactory]) => null;
+  dynamic getTopLevelInterface([Function responseFactory]) =>
+      responseFactory(null);
 
-  dynamic getTypeDefinition(String typeKey, [Function responseFactory]) => null;
+  dynamic getTypeDefinition(String typeKey, [Function responseFactory]) =>
+      responseFactory(null);
 
-  dynamic getAllTypeDefinitions([Function responseFactory]) => null;
+  dynamic getAllTypeDefinitions([Function responseFactory]) =>
+      responseFactory(null);
 }
 
 abstract class UrlResponseDiskCache {
@@ -1034,8 +1037,13 @@ class UrlResponseDiskCacheStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _UrlResponseDiskCacheServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _UrlResponseDiskCacheServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }