convert uri contributor to use new task model

pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart

Index: pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart
diff --git a/pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart b/pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart
index a6101da896566a1bd17093994a0049c4ae2f5eee..ad621fa77b8ab37e8cc2511afc6d57a7c2cfae4e 100644
--- a/pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart
+++ b/pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart
@@ -10,6 +10,7 @@ import 'package:analysis_server/src/provisional/completion/dart/completion_dart.
 import 'package:analysis_server/src/services/completion/dart/arglist_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart';
 import 'package:analysis_server/src/services/completion/dart/keyword_contributor.dart';
+import 'package:analysis_server/src/services/completion/dart/uri_contributor.dart';
 import 'package:plugin/plugin.dart';
 
 /**
@@ -69,6 +70,8 @@ class DartCompletionPlugin implements Plugin {
         () => new ArgListContributor());
     registerExtension(DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
         () => new KeywordContributor());
+    registerExtension(DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
+        () => new UriContributor());
   }
 
   /**