src/vs/editor/common/model/editStack.ts/MultiModelEditStackElement/heapSize
class MultiModelEditStackElement:	public heapSize(resource: URI): number {
		const key = uriGetComparisonKey(resource);
		if (this._editStackElementsMap.has(key)) {
			const editStackElement = this._editStackElementsMap.get(key)!;
			return editStackElement.heapSize();
		}
		return 0;
	}