src/vs/platform/instantiation/common/graph.ts/Graph/lookupOrInsertNode
class Graph:	lookupOrInsertNode(data: T): Node<T> {
		const key = this._hashFn(data);
		let node = this._nodes.get(key);

		if (!node) {
			node = new Node(key, data);
			this._nodes.set(key, node);
		}

		return node;
	}