Reduce duplicated code

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

Index: pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart
diff --git a/pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart b/pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart
index b5da3558f9e79c761dfac249922150647757b493..8f52453e04dd2264a1d180ba2560e568b80c99cb 100644
--- a/pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart
+++ b/pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart
@@ -8,7 +8,7 @@ import 'package:analysis_server/src/provisional/completion/dart/completion_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';
@@ -475,7 +475,7 @@ abstract class DartCompletionContributorTest extends AbstractContextTest {
     });
     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 =