Revert "dart2js: Avoid escaping in strings if it's not necessary."

tests/compiler/dart2js/string_escapes2_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 'dart:async';
-import 'package:async_helper/async_helper.dart';
-import 'package:expect/expect.dart';
-import 'compiler_helper.dart';
-
-// Test that the compiler doesn't escape too many characters.
-
-Future<String> compileExpression(String expression) {
-  var source = "foo() { return $expression; }";
-  return compile(source, entry: "foo");
-}
-
-Future runTest() {
-  return compileExpression(r"'Тест на Кирилица - great.\n"
-                           r'Next "line".\u2028'
-                           r'And another one.\u2029'
-                           r"and the last one'")
-      .then((String generated) {
-    Expect.isTrue(
-        generated.contains(r'"Тест на Кирилица - great.\n'
-                           r'Next \"line\".\u2028'
-                           r'And another one.\u2029'
-                           r'and the last one"') ||
-        generated.contains(r"'Тест на Кирилица - great.\n"
-                           r'Next "line".\u2028'
-                           r'And another one.\u2029'
-                           r"and the last one'"));
-  });
-}
-
-main() {
-  asyncTest(runTest);
-}