title: ng build error - Property 'requestMIDIAccess' does not exist
body: <p>I am trying to build an Angular2 project, using the Web Midi API. </p>
  
  <p>When running<code>ng build</code>, I am not able to complete the process due to certain errors thrown, specifically:</p>
  
  <pre>
  Error in bail mode: [default] /Users/JmsToh/GitHub/web-editor/web-editor/src/app/midi.service.ts:43:22 
  Property 'requestMIDIAccess' does not exist on type 'Navigator'.
  </pre>
  
  <p>This comes from this part of the code:</p>
  
  <pre><code>if (navigator.requestMIDIAccess) {
    this.browserMidiCompatible = true;
    navigator.requestMIDIAccess({ sysex: false })
      .then(this.onMIDISuccess.bind(this), this.onMIDIReject.bind(this));
  } else {
    alert("Platform not compatible");
  }
  </code></pre>
  
  <p>The app runs fine on Chrome when running <code>ng serve</code>.Is there any way to get Angular2 to ignore the error when building?</p>