src/vs/editor/browser/controller/mouseHandler.ts/MouseDownState/constructor
class MouseDownState:	constructor() {
		this._altKey = false;
		this._ctrlKey = false;
		this._metaKey = false;
		this._shiftKey = false;
		this._leftButton = false;
		this._middleButton = false;
		this._startedOnLineNumbers = false;
		this._lastMouseDownPosition = null;
		this._lastMouseDownPositionEqualCount = 0;
		this._lastMouseDownCount = 0;
		this._lastSetMouseDownCountTime = 0;
		this.isDragAndDrop = false;
	}