Use simple prefix/suffix diff in members sorter.

pkg/analysis_server/test/services/correction/diff_test.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.
+
+library test.services.correction.diff;
+
+import 'package:analysis_server/src/services/correction/diff.dart';
+import 'package:unittest/unittest.dart';
+
+import '../../reflective_tests.dart';
+
+
+main() {
+  groupSep = ' | ';
+  runReflectiveTests(DiffTest);
+}
+
+@ReflectiveTestCase()
+class DiffTest {
+  void test_findCommonPrefix() {
+    expect(findCommonPrefix('abc', 'xyz'), 0);
+    expect(findCommonPrefix('1234abcdef', '1234xyz'), 4);
+    expect(findCommonPrefix('123', '123xyz'), 3);
+  }
+
+  void test_findCommonSuffix() {
+    expect(findCommonSuffix('abc', 'xyz'), 0);
+    expect(findCommonSuffix('abcdef1234', 'xyz1234'), 4);
+    expect(findCommonSuffix('123', 'xyz123'), 3);
+  }
+}