message: Avoid clearing metric when saving from datasource editor
diff: @@ -2,6 +2,7 @@ import React from 'react';
  import PropTypes from 'prop-types';
  import VirtualizedSelect from 'react-virtualized-select';
  import { t } from '@superset-ui/translation';
  +import { isEqual } from 'lodash';
  import ControlHeader from '../ControlHeader';
  import VirtualizedRendererWrap from '../../../components/VirtualizedRendererWrap';
  @@ -117,8 +118,8 @@ export default class MetricsControl extends React.PureComponent {
  componentWillReceiveProps(nextProps) {
  if (
  - this.props.columns !== nextProps.columns ||
  - this.props.savedMetrics !== nextProps.savedMetrics
  + isEqual(this.props.columns) !== isEqual(nextProps.columns) ||
  + isEqual(this.props.savedMetrics) !== isEqual(nextProps.savedMetrics)
  ) {
  this.setState({ options: this.optionsForSelect(nextProps) });
  this.props.onChange([]);
  