title: Angular 4 disabled FormControl does not check or show validating errors
body: <p>I have <code>FormControl</code> object bind to <code>input</code> element.</p>
  
  <p><code>&lt;input matInput [formControl]="nameControl"&gt;</code></p>
  
  <p>It is initialized as follows</p>
  
  <p><code>this.nameControl = new FormControl({value: initValue, disabled: true}, [Validators.required, UniqueValueValidator(uniqueValues)]);</code></p>
  
  <p>When <code>FormControl</code> is disabled, it does not check for any errors.</p>
  
  <p>Question is how do I keep the control disabled and still show the errors.</p>