Let getDriverClass() handle defaults, so that extenders work. Also use it in...

Let getDriverClass() handle defaults, so that extenders work. Also use it in more places, eliminating the old-school crappy approach.

core/includes/Drupal/Database/Connection.php

@@ -589,7 +589,8 @@ protected function expandArguments(&$query, &$args) {
   public function getDriverClass($class) {
     if (empty($this->driverClasses[$class])) {
       $driver = $this->driver();
-      $this->driverClasses[$class] = "Drupal\\Database\\Driver\\{$driver}\\{$class}";
+      $driver_class = "Drupal\\Database\\Driver\\{$driver}\\{$class}";
+      $this->driverClasses[$class] = class_exists($driver_class) ? $driver_class : $class;
     }
     return $this->driverClasses[$class];
   }

core/includes/install.inc

@@ -1010,6 +1010,6 @@ function db_run_tasks($driver) {
  *   The name of the driver.
  */
 function db_installer_object($driver) {
-  $task_class = "Drupal\\Database\\Driver\\{$driver}\\Install\\Tasks";
-  return new $task_class();
+  $class = Database::getConnection()->getDriverClass('Install\\Tasks');
+  return new $class();
 }

core/modules/system/system.install

@@ -182,7 +182,7 @@ function system_requirements($phase) {
   }
   else {
     // Database information.
-    $class = 'DatabaseTasks_' . Database::getConnection()->driver();
+    $class = Database::getConnection()->getDriverClass('Install\\Tasks');
     $tasks = new $class();
     $requirements['database_system'] = array(
       'title' => $t('Database system'),