Add file missed in previous CL and comment clean-up

pkg/analysis_server/lib/plugin/completion.dart

Index: pkg/analysis_server/lib/plugin/completion.dart
diff --git a/pkg/analysis_server/lib/plugin/assist.dart b/pkg/analysis_server/lib/plugin/completion.dart
similarity index 56%
copy from pkg/analysis_server/lib/plugin/assist.dart
copy to pkg/analysis_server/lib/plugin/completion.dart
index cc037f6b087576f8b012c42a6b767dd37be074f3..623fa2b967d23159c9786b3d47958f1a368e5762 100644
--- a/pkg/analysis_server/lib/plugin/assist.dart
+++ b/pkg/analysis_server/lib/plugin/completion.dart
@@ -3,20 +3,20 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /**
- * Support for client code that extends the analysis server by adding new assist
- * contributors.
+ * Support for client code that extends the analysis server by adding new code
+ * completion contributors.
  */
-library analysis_server.plugin.assist;
+library analysis_server.plugin.completion;
 
-import 'package:analysis_server/edit/assist/assist_core.dart';
+import 'package:analysis_server/completion/completion_core.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analyzer/plugin/plugin.dart';
 
 /**
  * The identifier of the extension point that allows plugins to register new
- * assist contributors with the server. The object used as an extension must be
- * an [AssistContributor].
+ * code completion contributors with the server. The object used as an extension
+ * must be a [CompletionContributor].
  */
-final String ASSIST_CONTRIBUTOR_EXTENSION_POINT_ID = Plugin.join(
+final String COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID = Plugin.join(
     ServerPlugin.UNIQUE_IDENTIFIER,
-    ServerPlugin.ASSIST_CONTRIBUTOR_EXTENSION_POINT);
+    ServerPlugin.COMPLETION_CONTRIBUTOR_EXTENSION_POINT);