src/vs/editor/browser/controller/textAreaInput.ts/TextAreaInput/_setHasFocus
class TextAreaInput:	private _setHasFocus(newHasFocus: boolean): void {
		if (this._hasFocus === newHasFocus) {
			// no change
			return;
		}
		this._hasFocus = newHasFocus;

		if (this._selectionChangeListener) {
			this._selectionChangeListener.dispose();
			this._selectionChangeListener = null;
		}
		if (this._hasFocus) {
			this._selectionChangeListener = this._installSelectionChangeListener();
		}

		if (this._hasFocus) {
			this.writeScreenReaderContent('focusgain');
		}

		if (this._hasFocus) {
			this._onFocus.fire();
		} else {
			this._onBlur.fire();
		}
	}