src/vs/workbench/contrib/outline/browser/outlinePane.ts/OutlinePane/_captureViewState
class OutlinePane:	private _captureViewState(resource: URI | undefined): boolean {
		if (resource && this._tree) {
			const oldOutline = this._tree?.getInput();
			if (oldOutline) {
				this._treeStates.set(`${oldOutline.outlineKind}/${resource}`, this._tree!.getViewState());
				return true;
			}
		}
		return false;
	}