src/vs/platform/undoRedo/common/undoRedoService.ts/UndoRedoService/_tryToSplitAndUndo
class UndoRedoService:	private _tryToSplitAndUndo(strResource: string, element: WorkspaceStackElement, ignoreResources: RemovedResources | null, message: string): WorkspaceVerificationError {
		if (element.canSplit()) {
			this._splitPastWorkspaceElement(element, ignoreResources);
			this._notificationService.warn(message);
			return new WorkspaceVerificationError(this._undo(strResource, 0, true));
		} else {
			// Cannot safely split this workspace element => flush all undo/redo stacks
			for (const strResource of element.strResources) {
				this.removeElements(strResource);
			}
			this._notificationService.warn(message);
			return new WorkspaceVerificationError();
		}
	}