[WEB-16445] When create a missing imported library/part, add the edit once.

pkg/analysis_server/test/services/correction/fix_test.dart

Index: pkg/analysis_server/test/services/correction/fix_test.dart
diff --git a/pkg/analysis_server/test/services/correction/fix_test.dart b/pkg/analysis_server/test/services/correction/fix_test.dart
index 1b4af7d502dab1bbf60f7cf31a1d3e78bebac9db..f09f8c6f74229f3025449a126dcdcf2369c80e6c 100644
--- a/pkg/analysis_server/test/services/correction/fix_test.dart
+++ b/pkg/analysis_server/test/services/correction/fix_test.dart
@@ -1055,6 +1055,7 @@ import 'my_file.dart';
     SourceFileEdit fileEdit = change.edits[0];
     expect(fileEdit.file, '/my/project/bin/my_file.dart');
     expect(fileEdit.fileStamp, -1);
+    expect(fileEdit.edits, hasLength(1));
     expect(fileEdit.edits[0].replacement, contains('library my.file;'));
   }
 
@@ -1073,6 +1074,7 @@ part 'my_part.dart';
     SourceFileEdit fileEdit = change.edits[0];
     expect(fileEdit.file, '/my/project/bin/my_part.dart');
     expect(fileEdit.fileStamp, -1);
+    expect(fileEdit.edits, hasLength(1));
     expect(fileEdit.edits[0].replacement, contains('part of my.lib;'));
   }