title: MatDatepickerFilter - Filter function can't access class variable
body: <p>A MatDatePicker with a filter defined as followed:</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;mat-form-field class="example-full-width"&gt;
    &lt;input matInput [matDatepickerFilter]="myFilter" [matDatepicker]="picker" placeholder="Choose a date"&gt;
    &lt;mat-datepicker-toggle matSuffix [for]="picker"&gt;&lt;/mat-datepicker-toggle&gt;
    &lt;mat-datepicker #picker&gt;&lt;/mat-datepicker&gt;
  &lt;/mat-form-field&gt;
  </code></pre>
  
  <pre class="lang-typescript prettyprint-override"><code>export class DatepickerFilterExample {
    someDateToBlock: number = 3;
    myFilter = (d: Date): boolean =&gt; {
      const day = d.getDay();
      // THIS FUNCTION CANNOT ACCESS THE VARIABLE 'someDateToBlock'
      return day !== 0 &amp;&amp; day !== 6;
    }
  }
  </code></pre>
  
  <p>I would like to access the variable someDateToBlock (or any other) in the filter function. Is there a workaround to make this possbile?</p>