Fix for the prefix/suffix diff computing.

pkg/analysis_server/lib/src/services/correction/diff.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 diff;
-
-import 'dart:math';
-
-
-/**
- * Return the number of characters common to the start of [a] and [b].
- */
-int findCommonPrefix(String a, String b) {
-  int n = min(a.length, b.length);
-  for (int i = 0; i < n; i++) {
-    if (a.codeUnitAt(i) != b.codeUnitAt(i)) {
-      return i;
-    }
-  }
-  return n;
-}
-
-
-/**
- * Return the number of characters common to the end of [a] and [b].
- */
-int findCommonSuffix(String a, String b) {
-  int a_length = a.length;
-  int b_length = b.length;
-  int n = min(a_length, b_length);
-  for (int i = 1; i <= n; i++) {
-    if (a.codeUnitAt(a_length - i) != b.codeUnitAt(b_length - i)) {
-      return i - 1;
-    }
-  }
-  return n;
-}