Add gr-embed-dashboard element

In Polymer 1.x, the Shadow DOM polyfill requires using the Polymer.dom
API to achieve distribution. There is no way to notify a DOM mutation
happened after the fact. So, when embedding Polymer 1.x elements inside
an app that is not itself a Polymer app, placing arbitrary content
inside a <slot> is not possible.

This element is intended to be a workaround for the duration of
PolyGerrit's existence on Polymer 1.x to allow for slotting of the
<gr-create-change-help> element into the "empty-outgoing" slot of the
<gr-change-list>.

Change-Id: I32a5031df6fff10e3c441ecdf87c7b50d2073e34

polygerrit-ui/app/elements/change-list/gr-embed-dashboard/gr-embed-dashboard.html

@@ -0,0 +1,41 @@
+<!--
+@license
+Copyright (C) 2018 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.
+-->
+
+<link rel="import" href="../../../bower_components/polymer/polymer.html">
+
+<link rel="import" href="../../change-list/gr-change-list/gr-change-list.html">
+<link rel="import" href="../gr-create-change-help/gr-create-change-help.html">
+
+<dom-module id="gr-embed-dashboard">
+  <template>
+    <gr-change-list
+        show-star
+        account="[[account]]"
+        preferences="[[preferences]]"
+        sections="[[sections]]">
+      <div id="emptyOutgoing" slot="empty-outgoing">
+        <template is="dom-if" if="[[showNewUserHelp]]">
+          <gr-create-change-help></gr-create-change-help>
+        </template>
+        <template is="dom-if" if="[[!showNewUserHelp]]">
+          No changes
+        </template>
+      </div>
+    </gr-change-list>
+  </template>
+  <script src="gr-embed-dashboard.js"></script>
+</dom-module>

polygerrit-ui/app/elements/change-list/gr-embed-dashboard/gr-embed-dashboard.js

@@ -0,0 +1,29 @@
+/**
+ * @license
+ * Copyright (C) 2018 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.
+ */
+(function() {
+  'use strict';
+
+  Polymer({
+    is: 'gr-embed-dashboard',
+    properties: {
+      account: Object,
+      sections: Array,
+      preferences: Object,
+      showNewUserHelp: Boolean,
+    },
+  });
+})();

polygerrit-ui/app/embed/embed.html

@@ -25,7 +25,6 @@ limitations under the License.
 <link rel="import" href="../elements/core/gr-search-bar/gr-search-bar.html">
 <link rel="import" href="../elements/diff/gr-diff-view/gr-diff-view.html">
 <link rel="import" href="../elements/change-list/gr-change-list-view/gr-change-list-view.html">
-<link rel="import" href="../elements/change-list/gr-change-list/gr-change-list.html">
-<link rel="import" href="../elements/change-list/gr-create-change-help/gr-create-change-help.html">
 <link rel="import" href="../elements/change-list/gr-dashboard-view/gr-dashboard-view.html">
+<link rel="import" href="../elements/change-list/gr-embed-dashboard/gr-embed-dashboard.html">
 <link rel="import" href="../styles/themes/app-theme.html">