Bundle gr-diff and gr-diff-cursor components

gr-diff does not depend on gr-diff-cursor (because gr-diff-cursor can
handle multiple instances of gr-diff), but it's often useful when
embedding gr-diff to also have gr-diff-cursor available. This HTML file
can be used to bundle/vulcanize the two together to embed them into
another app.

Change-Id: I67092821cf86088429f887000e4271902ad92293

polygerrit-ui/app/embed/gr-diff.html

@@ -0,0 +1,25 @@
+<!--
+@license
+Copyright (C) 2019 The Android Open Source Project
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+<script>
+  // Needed for JSCompiler to understand it's global.
+  // eslint-disable-next-line no-unused-vars, prefer-const
+  let Gerrit = window.Gerrit || {};
+  window.Gerrit = Gerrit;
+</script>
+<link rel="import" href="../styles/themes/app-theme.html">
+<link rel="import" href="../elements/diff/gr-diff/gr-diff.html">
+<link rel="import" href="../elements/diff/gr-diff-cursor/gr-diff-cursor.html">