menu: trigger ExpressionChangedAfterItHasBeenCheckedError aria-expanded: null in OnPush component

#### What is the expected behavior?
Error should not occur

#### What is the current behavior?
Repeatedly and quickly clicking on menu trigger button causes error

#### What are the steps to reproduce?
[StackBlitz](https://stackblitz.com/edit/angular-stgyux)
Click on menuTrigger repeatedly -> error shows in console

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
Angular 7.1.0
Angular Material 7.1.0
Chrome Browser

#### Is there anything else we should know?
ChangeDetection: OnPush

ERROR
Error: ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value: 'aria-expanded: true'. Current value: 'aria-expanded: null'.

从链接的 StackBlitz 复现开始，使用 Angular 和 Angular Material 7.1.0，然后在观察控制台的同时，反复点击 OnPush 组件中的菜单触发器。跟踪菜单触发器的 aria-expanded 变化，并确定为什么已检查的值会变为 null；当复现不再报告 ExpressionChangedAfterItHasBeenCheckedError 时即表示完成。

由索引模型根据 Issue 内容生成。