Unify String.

runtime/lib/string_patch.dart

+// Copyright (c) 2012, 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.
+
+patch class StringImplementation {
+  /* patch */ static String _fromCharCodes(List<int> charCodes) {
+    return StringBase.createFromCharCodes(charCodes);
+  }
+
+  /* patch */ static String join(List<String> strings, String separator) {
+    return StringBase.join(strings, separator);
+  }
+
+  /* patch */ static String concatAll(List<String> strings) {
+    return StringBase.concatAll(strings);
+  }
+}