Use Configure to load plugin paths.

Switch to using more standard framework features to load the plugin
configuration file. This will also allow us to dump() to export files
from the plugin-installer.

src/Core/Plugin.php

@@ -15,6 +15,7 @@
 namespace Cake\Core;
 
 use Cake\Core\ClassLoader;
+use Cake\Core\Configure;
 use DirectoryIterator;
 
 /**
@@ -41,13 +42,6 @@ class Plugin
      */
     protected static $_loader;
 
-    /**
-     * The config map of plugins and their paths.
-     *
-     * @var array
-     */
-    protected static $_config;
-
     /**
      * Loads a plugin and optionally loads bootstrapping,
      * routing files or runs an initialization function.
@@ -125,8 +119,8 @@ public static function load($plugin, array $config = [])
             }
             return;
         }
-        if (static::$_config === null) {
-            static::_loadConfigMap();
+        if (!Configure::check('pluginPaths')) {
+            Configure::load('plugins');
         }
 
         $config += [
@@ -137,16 +131,16 @@ public static function load($plugin, array $config = [])
             'ignoreMissing' => false
         ];
 
-        if (!isset($config['path']) && isset(static::$_config[$plugin])) {
-            $config['path'] = static::$_config[$plugin];
+        if (!isset($config['path'])) {
+            $config['path'] = Configure::read('plugins.' . $plugin);
         }
 
         if (empty($config['path'])) {
             $paths = App::path('Plugin');
             foreach ($paths as $path) {
                 $pluginPath = str_replace('/', DS, $plugin);
                 if (is_dir($path . $pluginPath)) {
-                    $config += ['path' => $path . $pluginPath . DS];
+                    $config['path'] = $path . $pluginPath . DS;
                     break;
                 }
             }
@@ -183,24 +177,6 @@ public static function load($plugin, array $config = [])
         }
     }
 
-    /**
-     * Loads the config mappings for plugins.
-     *
-     * The map data in CONFIG/plugins.php map data is used set default paths
-     * for where plugins are located.
-     *
-     * @return void
-     */
-    protected static function _loadConfigMap()
-    {
-        if (!file_exists(CONFIG . 'plugins.php')) {
-            static::$_config = [];
-            return;
-        }
-        $config = include CONFIG . 'plugins.php';
-        static::$_config = $config;
-    }
-
     /**
      * Will load all the plugins located in the default plugin folder.
      *

tests/test_app/config/plugins.php

@@ -0,0 +1,4 @@
+<?php
+$config = [
+    'plugins' => []
+];