src/vs/platform/undoRedo/common/undoRedoService.ts/UndoRedoService/_pushElement
class UndoRedoService:	private _pushElement(element: StackElement): void {
		for (let i = 0, len = element.strResources.length; i < len; i++) {
			const resourceLabel = element.resourceLabels[i];
			const strResource = element.strResources[i];

			let editStack: ResourceEditStack;
			if (this._editStacks.has(strResource)) {
				editStack = this._editStacks.get(strResource)!;
			} else {
				editStack = new ResourceEditStack(resourceLabel, strResource);
				this._editStacks.set(strResource, editStack);
			}

			editStack.pushElement(element);
		}
	}