fix(chat): fix auto-scrolling to bottom

Empower the parent.

react/features/chat/components/web/Chat.js

      */
     _isExited: boolean;
 
+    /**
+     * Reference to the React Component for displaying chat messages. Used for
+     * scrolling to the end of the chat messages.
+     */
+    _messageContainerRef: Object;
+
     /**
      * Initializes a new {@code Chat} instance.
      *
         super(props);
 
         this._isExited = true;
+        this._messageContainerRef = React.createRef();
 
         // Bind event handlers so they are only bound once for every instance.
         this._renderPanelContent = this._renderPanelContent.bind(this);
     }
 
+    /**
+     * Implements {@code Component#componentDidMount}.
+     *
+     * @inheritdoc
+     */
+    componentDidMount() {
+        this._scrollMessageContainerToBottom(true);
+    }
+
+    /**
+     * Implements {@code Component#componentDidUpdate}.
+     *
+     * @inheritdoc
+     */
+    componentDidUpdate(prevProps) {
+        if (this.props._messages !== prevProps._messages) {
+            this._scrollMessageContainerToBottom(true);
+        } else if (this.props._isOpen && !prevProps._isOpen) {
+            this._scrollMessageContainerToBottom(false);
+        }
+    }
+
     /**
      * Implements React's {@link Component#render()}.
      *
     _renderChat() {
         return (
             <>
-                <MessageContainer messages = { this.props._messages } />
+                <MessageContainer
+                    messages = { this.props._messages }
+                    ref = { this._messageContainerRef } />
                 <ChatInput />
             </>
         );
             </div>
         );
     }
+
+    /**
+     * Scrolls the chat messages so the latest message is visible.
+     *
+     * @param {boolean} withAnimation - Whether or not to show a scrolling
+     * animation.
+     * @private
+     * @returns {void}
+     */
+    _scrollMessageContainerToBottom(withAnimation) {
+        if (this._messageContainerRef.current) {
+            this._messageContainerRef.current.scrollToBottom(withAnimation);
+        }
+    }
 }
 
 export default translate(connect(_mapStateToProps, _mapDispatchToProps)(Chat));

react/features/chat/components/web/MessageContainer.js

         this._messagesListEndRef = React.createRef();
     }
 
-    /**
-     * Implements React's {@link Component#componentDidMount()}.
-     *
-     * @inheritdoc
-     */
-    componentDidMount() {
-        this._scrollMessagesToBottom();
-    }
-
-    /**
-     * Updates chat input focus.
-     *
-     * @inheritdoc
-     */
-    componentDidUpdate() {
-        this._scrollMessagesToBottom();
-    }
-
     /**
      * Implements {@code Component#render}.
      *
         );
     }
 
-    _getMessagesGroupedBySender: () => Array<Array<Object>>;
-
     /**
      * Automatically scrolls the displayed chat messages down to the latest.
      *
-     * @private
+     * @param {boolean} withAnimation - Whether or not to show a scrolling
+     * animation.
      * @returns {void}
      */
-    _scrollMessagesToBottom() {
+    scrollToBottom(withAnimation: boolean) {
         this._messagesListEndRef.current.scrollIntoView({
-            behavior: 'smooth'
+            behavior: withAnimation ? 'smooth' : 'auto'
         });
     }
+
+    _getMessagesGroupedBySender: () => Array<Array<Object>>;
 }