src/vs/editor/browser/controller/mouseHandler.ts/MouseHandler/_onMouseLeave
class MouseHandler:	public _onMouseLeave(e: EditorMouseEvent): void {
		if (this._mouseLeaveMonitor) {
			this._mouseLeaveMonitor.dispose();
			this._mouseLeaveMonitor = null;
		}
		this.lastMouseLeaveTime = (new Date()).getTime();
		this.viewController.emitMouseLeave({
			event: e,
			target: null
		});
	}