src/vs/platform/extensionManagement/node/extensionManagementService.ts/ExtensionsScanner/setInstalled
class ExtensionsScanner:	async setInstalled(extensionKey: ExtensionKey): Promise<ILocalExtension | null> {
		await this.withUninstalledExtensions(uninstalled => delete uninstalled[extensionKey.toString()]);
		const userExtensions = await this.scanUserExtensions(true);
		const localExtension = userExtensions.find(i => ExtensionKey.create(i).equals(extensionKey)) || null;
		if (!localExtension) {
			return null;
		}
		return this.updateMetadata(localExtension, { installedTimestamp: Date.now() });
	}