message: [sql lab] fix sluggish backspace in editor
  Somehow Ace's "changeSelection" event is triggered when hitting
  backspace (and shouldn't!).
  changeSelection on our side triggers enough work to make the
  holding backspace sluggish and laggy.
  This fix ignores selection with a length of 1, avoiding mutating the
  state altogether when hitting/holding backspace.
diff: @@ -45,6 +45,7 @@ class AceEditorWrapper extends React.PureComponent {
  super(props);
  this.state = {
  sql: props.sql,
  + selectedText: '',
  };
  }
  componentDidMount() {
  @@ -77,8 +78,13 @@ class AceEditorWrapper extends React.PureComponent {
  });
  editor.$blockScrolling = Infinity; // eslint-disable-line no-param-reassign
  editor.selection.on('changeSelection', () => {
  + const selectedText = editor.getSelectedText();
  + // Backspace trigger 1 character selection, ignoring
  + if (selectedText !== this.state.selectedText && selectedText.length !== 1) {
  + this.setState({ selectedText });
  this.props.actions.queryEditorSetSelectedText(
  - this.props.queryEditor, editor.getSelectedText());
  + this.props.queryEditor, selectedText);
  + }
  });
  }
  getCompletions(aceEditor, session, pos, prefix, callback) {
  