Merge more Kernel infrastructure from kernel_sdk SDK fork.

runtime/lib/regexp_patch.dart

Index: runtime/lib/regexp_patch.dart
diff --git a/runtime/lib/regexp_patch.dart b/runtime/lib/regexp_patch.dart
index 7e8bc194998bc87e03a34545c7f33797eb1f6035..a9ccd55527ec503550ee2969c974b6a4d04c68fc 100644
--- a/runtime/lib/regexp_patch.dart
+++ b/runtime/lib/regexp_patch.dart
@@ -2,8 +2,6 @@
 // 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:collection" show LinkedList, LinkedListEntry;
-
 @patch class RegExp {
   @patch factory RegExp(String source,
                               {bool multiLine: false,