Declare `multisite` as a field for `WP_Object_Cache`.

See #30799.


git-svn-id: https://develop.svn.wordpress.org/trunk@31682 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/cache.php

@@ -103,7 +103,7 @@ function wp_cache_flush() {
  * @param int|string $key What the contents in the cache are called
  * @param string $group Where the cache contents are grouped
  * @param bool $force Whether to force an update of the local cache from the persistent cache (default is false)
- * @param &bool $found Whether key was found in the cache. Disambiguates a return of false, a storable value.
+ * @param bool &$found Whether key was found in the cache. Disambiguates a return of false, a storable value.
  * @return bool|mixed False on failure to retrieve contents or the cache
  *		contents on success
  */
@@ -305,6 +305,15 @@ class WP_Object_Cache {
 	 */
 	private $blog_prefix;
 
+	/**
+	 * Holds the value of `is_multisite()`
+	 *
+	 * @var bool
+	 * @access private
+	 * @since 3.5.0
+	 */
+	private $multisite;
+
 	/**
 	 * Make private properties readable for backwards compatibility.
 	 *