Used writer instead of protected methods to add and remove the link h…

…ighlight.

src/linkediting.js

@@ -19,7 +19,7 @@ import bindTwoStepCaretToAttribute from '@ckeditor/ckeditor5-engine/src/utils/bi
 import findLinkRange from './findlinkrange';
 import '../theme/link.css';
 
-const HIGHLIGHT_CLASSES = 'ck ck-link_selected';
+const HIGHLIGHT_CLASSES = [ 'ck', 'ck-link_selected' ];
 
 /**
  * The link engine feature.
@@ -88,16 +88,16 @@ export default class LinkEditing extends Plugin {
 		const highlightedLinks = new Set();
 
 		// Adding the class.
-		viewDocument.registerPostFixer( () => {
+		viewDocument.registerPostFixer( writer => {
 			const selection = modelDocument.selection;
 
 			if ( selection.hasAttribute( 'linkHref' ) ) {
 				const modelRange = findLinkRange( selection.getFirstPosition(), selection.getAttribute( 'linkHref' ) );
 				const viewRange = editor.editing.mapper.toViewRange( modelRange );
 
 				for ( const item of viewRange.getItems() ) {
-					if ( item.is( 'attributeElement' ) && item.name == 'a' ) {
-						item._addClass( HIGHLIGHT_CLASSES );
+					if ( item.is( 'a' ) ) {
+						writer.addClass( HIGHLIGHT_CLASSES, item );
 						highlightedLinks.add( item );
 					}
 				}
@@ -113,9 +113,9 @@ export default class LinkEditing extends Plugin {
 
 		// Removing the class.
 		function removeHighlight() {
-			view.change( () => {
+			view.change( writer => {
 				for ( const linkElement of highlightedLinks.values() ) {
-					linkElement._removeClass( HIGHLIGHT_CLASSES );
+					writer.removeClass( HIGHLIGHT_CLASSES, linkElement );
 					highlightedLinks.delete( linkElement );
 				}
 			} );