Extract 'computeLineStarts' utility.

pkg/analyzer/lib/src/generated/utilities_string.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 engine.utilities.string;
+
+/**
+ * Compute line starts for the given [content].
+ * Lines end with `\r`, `\n` or `\r\n`.
+ */
+List<int> computeLineStarts(String content) {

[Brian Wilkerson, 2015/10/27 20:44:10]

Could we add it to StringUtilities so that there's only one place to have to
remember to look for utilities?

+  List<int> lineStarts = <int>[0];
+  int length = content.length;
+  int unit;
+  for (int index = 0; index < length; index++) {
+    unit = content.codeUnitAt(index);
+    // Special-case \r\n.
+    if (unit == 0x0D /* \r */) {
+      // Peek ahead to detect a following \n.
+      if ((index + 1 < length) && content.codeUnitAt(index + 1) == 0x0A) {
+        // Line start will get registered at next index at the \n.
+      } else {
+        lineStarts.add(index + 1);
+      }
+    }
+    // \n
+    if (unit == 0x0A) {
+      lineStarts.add(index + 1);
+    }
+  }
+  return lineStarts;
+}