Add quoteRegExp() to utils.

sdk/lib/_internal/pub/test/serve/warns_on_assets_paths_test.dart

Index: sdk/lib/_internal/pub/test/serve/warns_on_assets_paths_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/warns_on_assets_paths_test.dart b/sdk/lib/_internal/pub/test/serve/warns_on_assets_paths_test.dart
index c4ae0c5dd1a53ac0370d2d621bb3ddd901fa15c5..e77af93391e3367b814c17ab9fb7614a50c506e1 100644
--- a/sdk/lib/_internal/pub/test/serve/warns_on_assets_paths_test.dart
+++ b/sdk/lib/_internal/pub/test/serve/warns_on_assets_paths_test.dart
@@ -7,13 +7,14 @@ library pub_tests;
 import 'package:path/path.dart' as path;
 import 'package:scheduled_test/scheduled_test.dart';
 
+import '../../lib/src/utils.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import 'utils.dart';
 
 getWarningRegExp(String assetsPath) {
   // Escape backslashes since they are metacharacters in a regex.
-  assetsPath = assetsPath.replaceAll("\\", "\\\\");
+  assetsPath = quoteRegExp(assetsPath);
   return new RegExp(
       '^Warning: Pub reserves paths containing "assets" for using assets from '
       'packages\\. Please rename the path "$assetsPath"\\.\$');