src/vs/editor/browser/controller/mouseHandler.ts/MouseDownState/setModifiers
class MouseDownState:	public setModifiers(source: EditorMouseEvent) {
		this._altKey = source.altKey;
		this._ctrlKey = source.ctrlKey;
		this._metaKey = source.metaKey;
		this._shiftKey = source.shiftKey;
	}