Add third_party/liburlpattern directory.

This creates an empty directory to be used to write the liburlpattern
code.  This library will be the URL pattern matching engine for the
URLPattern web API being developed in:

  https://github.com/wicg/urlpattern

The pattern syntax is based on the populat path-to-regexp library:

  https://github.com/pillarjs/path-to-regexp

This is being developed as a separate library so that it can be a
derivitive work of path-to-regexp using an MIT license.  No code from
path-to-regexp will be directly included here.

Bug: 1141510
Change-Id: Ia695bf927c40723b3d5adc171fd2b8d3bb879772
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2486388Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821791}

third_party/liburlpattern/LICENSE

+The MIT License (MIT)
+
+Copyright (c) 2020 The Chromium Authors. All rights reserved.
+Copyright (c) 2014 Blake Embrey (hello@blakeembrey.com)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

third_party/liburlpattern/OWNERS

+# primary
+wanderview@chromium.org
+
+# secondary
+shimazu@chromium.org
+jbroman@chromium.org
+
+# TEAM: worker-dev@chromium.org
+# COMPONENT: Blink>ServiceWorker

third_party/liburlpattern/README.chromium

+Name: URL Pattern Library
+Short Name: liburlpattern
+URL: https://chromium.googlesource.com/chromium/src/+/HEAD/third_party/liburlpattern
+Version: 0
+License: MIT
+Security Critical: yes
+
+Description:
+This library is the underlying pattern matching engine for the URLPattern web
+API proposal being discussed in https://github.com/wicg/urlpattern.  It uses
+a pattern syntax derived from the path-to-regexp library developed at
+https://github.com/pillarjs/path-to-regexp.  It is developed by the chromium
+project, but licensed as a derivative work of path-to-regexp using an MIT
+license.  No code from path-to-regexp is directly used here.