[IMP] mail: Add icon in chat windows to expand in discuss

addons/mail/static/src/js/extended_chat_window.js

 odoo.define('mail.ExtendedChatWindow', function (require) {
 "use strict";
 
+var core = require('web.core');
+
 var chat_manager = require('mail.chat_manager');
 var ChatWindow = require('mail.ChatWindow');
 var composer = require('mail.composer');
 
 return ChatWindow.extend({
     template: "mail.ExtendedChatWindow",
-
+    events: _.extend({}, ChatWindow.prototype.events, {
+        "click .o_chat_window_expand": "on_click_expand",
+    }),
     start: function () {
         var self = this;
         var def;
@@ -44,6 +48,13 @@ return ChatWindow.extend({
     on_keydown: function (event) {
         event.stopPropagation();
     },
+    on_click_expand: _.debounce(function () {
+        event.preventDefault();
+        var options = {clear_breadcrumbs: true, active_id: this.channel_id};
+        this.do_action('mail.mail_channel_action_client_chat', options).then(function () {
+            core.bus.trigger('change_menu_section', chat_manager.get_discuss_menu_id());
+        });
+    }, 1000, true),
 });
 
 });

addons/mail/static/src/less/chat_window.less

@@ -47,7 +47,7 @@
             .o-text-overflow();
         }
 
-        .o_chat_window_close {
+        .o_chat_window_close, .o_chat_window_expand {
             color: white;
             padding: 3px;
             margin-left: 5px;

addons/mail/static/src/xml/extended_chat_window.xml

@@ -10,4 +10,11 @@
         </t>
     </t>
 
+    <t t-extend="mail.ChatWindowHeaderContent">
+        <t t-jquery=".o_chat_window_close" t-operation="before">
+            <a href="#" class="o_chat_window_expand fa fa-expand" title="
+            Open in Discuss"/>
+        </t>
+    </t>
+
 </templates>