src/vs/editor/browser/widget/codeEditorWidget.ts/CodeEditorWidgetFocusTracker/constructor
class CodeEditorWidgetFocusTracker:	constructor(domElement: HTMLElement) {
		super();

		this._hasFocus = false;
		this._domFocusTracker = this._register(dom.trackFocus(domElement));

		this._register(this._domFocusTracker.onDidFocus(() => {
			this._hasFocus = true;
			this._onChange.fire(undefined);
		}));
		this._register(this._domFocusTracker.onDidBlur(() => {
			this._hasFocus = false;
			this._onChange.fire(undefined);
		}));
	}