Extract 'computeLineStarts' utility.

pkg/analyzer/test/generated/utilities_string_test.dart

+// Copyright (c) 2015, 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.engine.utilities.string;
+
+import 'package:analyzer/src/generated/utilities_string.dart';
+import 'package:unittest/unittest.dart';
+
+import '../reflective_tests.dart';
+import '../utils.dart';
+
+main() {
+  initializeTestEnvironment();
+  runReflectiveTests(ComputeLineStartsTest);
+}
+
+@reflectiveTest
+class ComputeLineStartsTest {
+  void test_n() {
+    List<int> starts = computeLineStarts('a\nbb\nccc');
+    expect(starts, <int>[0, 2, 5]);
+  }
+
+  void test_r() {
+    List<int> starts = computeLineStarts('a\rbb\rccc');
+    expect(starts, <int>[0, 2, 5]);
+  }
+
+  void test_rn() {
+    List<int> starts = computeLineStarts('a\r\nbb\r\nccc');
+    expect(starts, <int>[0, 3, 7]);
+  }
+}