Update the plugin API

pkg/analyzer_plugin/lib/src/utilities/completion/completion_core.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/utilities/completion/completion_core.dart';
 
 /**
@@ skipping 44 matching lines @@
 
   @override
   void set offset(int length) {
     if (_offset != null) {
       throw new StateError('The offset can only be set once');
     }
     _offset = length;
   }
 
   @override
-  void addSuggestion(CompletionSuggestion suggestion) {
-    suggestions.add(suggestion);
-  }
-
-  @override
   bool get offsetIsSet => offset != null;
 
   @override
   int get suggestionsLength => suggestions.length;
+
+  @override
+  void addSuggestion(CompletionSuggestion suggestion) {
+    suggestions.add(suggestion);
+  }
 }
 
 /**
- * Information about the completion request that was made.
- */
-class CompletionRequestImpl implements CompletionRequest {
+* A concrete implementation of [DartCompletionRequest].
+*/
+class DartCompletionRequestImpl implements DartCompletionRequest {
+  @override
+  final ResourceProvider resourceProvider;
+
   @override
   final int offset;
 
   @override
-  final ResourceProvider resourceProvider;
-
-  @override
   final ResolveResult result;
 
   /**
    * A flag indicating whether completion has been aborted.
    */
   bool _aborted = false;
 
   /**
    * Initialize a newly created request.
    */
-  CompletionRequestImpl(this.resourceProvider, this.result, this.offset);
+  DartCompletionRequestImpl(this.resourceProvider, this.offset, this.result);
 
   /**
    * Abort the current completion request.
    */
   void abort() {
     _aborted = true;
   }
 
   @override
   void checkAborted() {
     if (_aborted) {
       throw new AbortCompletion();
     }
   }
 }