requestMediaKeySystemAccess method
      
Future<MediaKeySystemAccess> 
requestMediaKeySystemAccess(
    
    
- String keySystem,
- Iterable<MediaKeySystemConfiguration> supportedConfigurations
Implementation
Future<MediaKeySystemAccess> requestMediaKeySystemAccess(String keySystem,
        Iterable<MediaKeySystemConfiguration> supportedConfigurations) =>
    js_util.promiseToFuture(js_util.callMethod(this,
        'requestMediaKeySystemAccess', [keySystem, supportedConfigurations]));