address comments

Author: mmalerba

src/material-experimental/mdc-list/list-base.ts

@@ -20,6 +20,14 @@ import {RippleConfig, RippleRenderer, RippleTarget, setLines} from '@angular/mat
 import {Subscription} from 'rxjs';
 import {startWith} from 'rxjs/operators';
 
+function toggleClass(el: Element, className: string, on: boolean) {
+  if (on) {
+    el.classList.add(className);
+  } else {
+    el.classList.remove(className);
+  }
+}
+
 @Directive()
 /** @docs-private */
 export abstract class MatListBase {
@@ -69,9 +77,9 @@ export abstract class MatListItemBase implements AfterContentInit, OnDestroy, Ri
       this._subscriptions.add(this.lines.changes.pipe(startWith(this.lines))
           .subscribe((lines: QueryList<ElementRef<Element>>) => {
             lines.forEach((line: ElementRef<Element>, index: number) => {
-              line.nativeElement.classList
-                  .toggle('mdc-list-item__primary-text', index === 0 && lines.length > 1);
-              line.nativeElement.classList.toggle('mdc-list-item__secondary-text', index !== 0);
+              toggleClass(line.nativeElement,
+                  'mdc-list-item__primary-text', index === 0 && lines.length > 1);
+              toggleClass(line.nativeElement, 'mdc-list-item__secondary-text', index !== 0);
             });
             setLines(lines, this._element, 'mat-mdc');
           }));

src/material-experimental/mdc-list/list-item.html

@@ -9,7 +9,7 @@
   If lines were not explicitly given, assume the remaining content is the text, otherwise assume it
   is an action that belongs in the "meta" section.
 -->
-<span [class.mdc-list-item__text]="!lines.length" [class.mdc-list-item__meta]="!!lines.length">
+<span [class.mdc-list-item__text]="!lines.length" [class.mdc-list-item__meta]="lines.length">
   <ng-content></ng-content>
 </span>