private function installPluginIfNecessary(Plugin $plugin)
    {
        $pluginName = $plugin->getPluginName();
        $saveConfig = false;

        // is the plugin already installed or is it the first time we activate it?
        $pluginsInstalled = $this->getInstalledPluginsName();

        if (!$this->isPluginInstalled($pluginName)) {
            $this->executePluginInstall($plugin);
            $pluginsInstalled[] = $pluginName;
            $this->updatePluginsInstalledConfig($pluginsInstalled);
            $updater = new Updater();
            $updater->markComponentSuccessfullyUpdated($plugin->getPluginName(), $plugin->getVersion(), $isNew = true);
            $saveConfig = true;

            /**
             * Event triggered after a new plugin has been installed.
             *
             * Note: Might be triggered more than once if the config file is not writable
             *
             * @param string $pluginName The plugin that has been installed.
             */
            Piwik::postEvent('PluginManager.pluginInstalled', array($pluginName));
        }

        if ($saveConfig) {
            PiwikConfig::getInstance()->forceSave();
            $this->clearCache($pluginName);
        }
    }