Add interface and use trait to make the config service a cacheable de…

…pendency... (#41)

... really, just inheriting cachability from the config at which it points.

src/Config.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\openseadragon;
 
+use Drupal\Core\Cache\RefinableCacheableDependencyTrait;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -12,6 +13,8 @@
  */
 class Config implements ConfigInterface {
 
+  use RefinableCacheableDependencyTrait;
+
   /**
    * The openseadragon config.
    *
@@ -49,6 +52,7 @@ class Config implements ConfigInterface {
   public function __construct(ConfigFactoryInterface $configFactory) {
     $this->config = $configFactory->get(Config::$configName);
     $this->configFactory = $configFactory;
+    $this->addCacheableDependency($this->config);
   }
 
   /**

src/ConfigInterface.php

@@ -2,13 +2,15 @@
 
 namespace Drupal\openseadragon;
 
+use Drupal\Core\Cache\CacheableDependencyInterface;
+
 /**
  * Special config class.
  *
  * This class allows the default config structure to remain, this is used to
  * clean up the settings form values and remove extra unnecessary arrays.
  */
-interface ConfigInterface {
+interface ConfigInterface extends CacheableDependencyInterface {
 
   /**
    * Get the default viewer settings.