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