Fix handling of CRLF line endings in Script::GetSnippet.

tests/lib/mirrors/method_mirror_source_line_ending_cr.dart

Index: tests/lib/mirrors/method_mirror_source_line_ending_cr.dart
diff --git a/tests/lib/mirrors/method_mirror_source_line_ending_cr.dart b/tests/lib/mirrors/method_mirror_source_line_ending_cr.dart
new file mode 100755
index 0000000000000000000000000000000000000000..851c04cf86c6f2c9f84a57000029b235fa9a2761
--- /dev/null
+++ b/tests/lib/mirrors/method_mirror_source_line_ending_cr.dart
@@ -0,0 +1 @@
+// 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.
// This file is marked executable so source control will preserve the type of
// line ending.
library line_endings.cr;
oneLineCR(x) => x;
multiLineCR(y) {
  return y + 1;
}
b
(){
}