Add tests for problem with newline encoding in multiline strings.

tests/language/multiline_newline_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.
+
+import 'package:expect/expect.dart';
+import 'multiline_newline_cr.dart' as cr;
+import 'multiline_newline_crlf.dart' as crlf;
+import 'multiline_newline_lf.dart' as lf;
+
+main() {
+  Expect.equals(4, cr.constantMultilineString.length);
+  Expect.equals(4, crlf.constantMultilineString.length);
+  Expect.equals(4, lf.constantMultilineString.length);
+  Expect.equals(cr.constantMultilineString, crlf.constantMultilineString);
+  Expect.equals(crlf.constantMultilineString, lf.constantMultilineString);
+  Expect.equals(lf.constantMultilineString, cr.constantMultilineString);
+
+  Expect.equals(4, cr.nonConstantMultilineString.length);
+  Expect.equals(4, crlf.nonConstantMultilineString.length);
+  Expect.equals(4, lf.nonConstantMultilineString.length);
+  Expect.equals(cr.nonConstantMultilineString, crlf.nonConstantMultilineString);
+  Expect.equals(crlf.nonConstantMultilineString, lf.nonConstantMultilineString);
+  Expect.equals(lf.nonConstantMultilineString, cr.nonConstantMultilineString);
+
+  const c1 =
+      cr.constantMultilineString == crlf.constantMultilineString ? true : null;
+  const c2 =
+      crlf.constantMultilineString == lf.constantMultilineString ? true : null;
+  const c3 =
+      lf.constantMultilineString == cr.constantMultilineString ? true : null;
+  Expect.isTrue(c1);
+  Expect.isTrue(c2);
+  Expect.isTrue(c3);
+
+  const c4 = c1 ? 1 : 2;  /// 01: ok
+  Expect.equals(1, c4);   /// 01: continued
+
+  const c5 = c2 ? 2 : 3;  /// 02: ok
+  Expect.equals(2, c5);   /// 02: continued
+
+  const c6 = c3 ? 3 : 4;  /// 03: ok
+  Expect.equals(3, c6);   /// 03: continued
+
+  const c7 =
+      cr.constantMultilineString != crlf.constantMultilineString ? true : null;
+  const c8 =
+      crlf.constantMultilineString != lf.constantMultilineString ? true : null;
+  const c9 =
+      lf.constantMultilineString != cr.constantMultilineString ? true : null;
+  Expect.isNull(c7);
+  Expect.isNull(c8);
+  Expect.isNull(c9);
+
+  const c10 = c7 ? 1 : 2;  /// 04: compile-time error
+  const c11 = c8 ? 2 : 3;  /// 05: compile-time error
+  const c12 = c9 ? 3 : 4;  /// 06: compile-time error
+}