title: @Viewchild can not see matSort
body: <p>In my Angular application, my @ViewChild instance is failing to fill HTL matSort.</p>
  
  <p><strong>mycomponent.ts:</strong></p>
  
  <pre><code>import { MatSort } from '@angular/material';
  
  export class MyClassComponent {
       @ViewChild(MatSort) sort: MatSort;
  
  }
  
  ngOnInit() {
      console.log(this.sort); // undefined
  }
  </code></pre>
  
  <p><strong>mycomponent.html:</strong></p>
  
  <pre><code>&lt;mat-table #table [dataSource]="dataSource" matSort&gt;
             .......................................................
             .......................................................
  
  &lt;/mat-table&gt;
  </code></pre>
  
  <p>I need to use sortChange from matSort but it is always returned undefined.</p>