Reduce duplicated code

pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart

 // Copyright (c) 2014, 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 'dart:async';
 
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/completion_core.dart';
 import 'package:analysis_server/src/services/completion/completion_performance.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart'
-    show DartCompletionRequestImpl, ReplacementRange;
+    show DartCompletionRequestImpl;
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/source/package_map_resolver.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
 
 import '../../../abstract_context.dart';
 import '../../correction/flutter_util.dart';
 
@@ skipping 446 matching lines @@
     // Build the request
     Completer<DartCompletionRequest> requestCompleter =
         new Completer<DartCompletionRequest>();
     DartCompletionRequestImpl
         .from(baseRequest)
         .then((DartCompletionRequest request) {
       requestCompleter.complete(request);
     });
     request = await performAnalysis(times, requestCompleter);
 
-    var range = new ReplacementRange.compute(request.offset, request.target);
+    var range = request.target.computeReplacementRange(request.offset);
     replacementOffset = range.offset;
     replacementLength = range.length;
     Completer<List<CompletionSuggestion>> suggestionCompleter =
         new Completer<List<CompletionSuggestion>>();
 
     // Request completions
     contributor
         .computeSuggestions(request)
         .then((List<CompletionSuggestion> computedSuggestions) {
       suggestionCompleter.complete(computedSuggestions);
@@ skipping 91 matching lines @@
     addSource(path, content);
   }
 
   @override
   void setUp() {
     super.setUp();
     testFile = provider.convertPath('/completionTest.dart');
     contributor = createContributor();
   }
 }