src/vs/workbench/services/extensionManagement/common/extensionManagementService.ts/ExtensionManagementService/download
class ExtensionManagementService:	download(extension: IGalleryExtension, operation: InstallOperation): Promise<URI> {
		if (this.extensionManagementServerService.localExtensionManagementServer) {
			return this.extensionManagementServerService.localExtensionManagementServer.extensionManagementService.download(extension, operation);
		}
		throw new Error('Cannot download extension');
	}