The error event on `<source>` elements doesn't work. Looking at #4370, it seems like there is an `onError` for `<video>` but I can't tell if that's supposed to work for `<source>` too.

The error event is useful so I can deduce which format the browser is using.

var contentToUse =
        CONTENT_TYPES[typeof props.children] ? props.children : null;
      var childrenToUse = contentToUse != null ? null : props.children;
      if (contentToUse != null) {
        
        ret = escapeTextContentForBrowser(contentToUse);
        if (__DEV__) {
          setContentChildForInstrumentation.call(this, contentToUse);
        }
      } else if (childrenToUse != null) {
        var mountImages = this.mountChildren(
          childrenToUse,
          transaction,
          context
        );
        ret = mountImages.join('');
      }
    }
    if (newlineEatingTags[this._tag] && ret.charAt(0) === '\n') {
      
      
      
      
      
      
      
      
      
      
      return '\n' + ret;