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.

}
    }
    for (propKey in nextProps) {
      var nextProp = nextProps[propKey];
      var lastProp =
        propKey === STYLE ? this._previousStyleCopy :
        lastProps != null ? lastProps[propKey] : undefined;
      if (!nextProps.hasOwnProperty(propKey) ||
          nextProp === lastProp ||
          nextProp == null && lastProp == null) {
        continue;
      }
      if (propKey === STYLE) {
        if (nextProp) {
          if (__DEV__) {
            checkAndWarnForMutatedStyle(
              this._previousStyleCopy,
              this._previousStyle,
              this
            );
            this._previousStyle = nextProp;
          }
          nextProp = this._previousStyleCopy = Object.assign({}, nextProp);
        } else {
          this._previousStyleCopy = null;
        }
        if (lastProp) {
          
          for (styleName in lastProp) {
            if (lastProp.hasOwnProperty(styleName) &&