src/vs/workbench/services/configuration/browser/configuration.ts/WorkspaceConfiguration/setFolders
class WorkspaceConfiguration:	setFolders(folders: IStoredWorkspaceFolder[], jsonEditingService: JSONEditingService): Promise<void> {
		if (this._workspaceIdentifier) {
			return jsonEditingService.write(this._workspaceIdentifier.configPath, [{ path: ['folders'], value: folders }], true)
				.then(() => this.reload());
		}
		return Promise.resolve();
	}