src/vs/editor/browser/controller/mouseHandler.ts/TopBottomDragScrolling/start
class TopBottomDragScrolling:	public start(position: IMouseTargetOutsideEditor, mouseEvent: EditorMouseEvent): void {
		if (this._operation) {
			this._operation.setPosition(position, mouseEvent);
		} else {
			this._operation = new TopBottomDragScrollingOperation(this._context, this._viewHelper, this._mouseTargetFactory, this._dispatchMouse, position, mouseEvent);
		}
	}