diff -u b/core/includes/file.inc b/core/includes/file.inc
--- b/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -921,7 +921,7 @@
  *   The file id.
  *
  * @see file_unmanaged_delete()
- * @see file_usage()->list_usage()
+ * @see file_usage()->listUsage()
  */
 function file_delete($fid) {
   return file_delete_multiple(array($fid));
@@ -938,7 +938,7 @@
  *   The file id.
  *
  * @see file_unmanaged_delete()
- * @see file_usage()->list_usage()
+ * @see file_usage()->listUsage()
  */
 function file_delete_multiple(array $fids) {
   entity_delete_multiple('file', $fids);
diff -u b/core/lib/Drupal/Core/CoreBundle.php b/core/lib/Drupal/Core/CoreBundle.php
--- b/core/lib/Drupal/Core/CoreBundle.php
+++ b/core/lib/Drupal/Core/CoreBundle.php
@@ -55,7 +55,8 @@
       ->setFactoryMethod('getConnection')
       ->addArgument('slave');
     $container->register('typed_data', 'Drupal\Core\TypedData\TypedDataManager');
-    $container->register('file.usage', 'Drupal\Core\FileUsage\DatabaseFileUsageBackend');
+    $container->register('file.usage', 'Drupal\Core\FileUsage\DatabaseFileUsageBackend')
+      ->addArgument(new Reference('database'));
 
     $container->register('router.dumper', '\Drupal\Core\Routing\MatcherDumper')
       ->addArgument(new Reference('database'));
diff -u b/core/lib/Drupal/Core/FileUsage/DatabaseFileUsageBackend.php b/core/lib/Drupal/Core/FileUsage/DatabaseFileUsageBackend.php
--- b/core/lib/Drupal/Core/FileUsage/DatabaseFileUsageBackend.php
+++ b/core/lib/Drupal/Core/FileUsage/DatabaseFileUsageBackend.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Database\DatabaseExceptionWrapper;
 use Drupal\file\File as File;
+use Drupal\Core\Database\Connection;
 
 /**
  * Defines the database file usage backend. This is the default Drupal backend.
@@ -16,10 +17,23 @@
 class DatabaseFileUsageBackend extends FileUsageBase {
 
   /**
+   * Construct the DatabaseFileUsageBackend.
+   *
+   * @param Drupal\Core\Database\Connection $connection
+   *   The database connection which will be used to store the route
+   *   information.
+   * @param string $table
+   *   (optional) The table to store the route info in. Defaults to 'router'.
+   */
+  public function __construct(Connection $connection) {
+    $this->connection = $connection;
+  }
+
+  /**
    * Implements Drupal\Core\FileUsage\FileUsageInterface::add().
    */
-  function add(File $file, $module, $type, $id, $count = 1) {
-    db_merge('file_usage')
+  public function add(File $file, $module, $type, $id, $count = 1) {
+    $this->connection->merge('file_usage')
       ->key(array(
         'fid' => $file->fid,
         'module' => $module,
@@ -36,9 +50,9 @@
   /**
    * Implements Drupal\Core\FileUsage\FileUsageInterface::delete().
    */
-  function delete(File $file, $module, $type = NULL, $id = NULL, $count = 1) {
+  public function delete(File $file, $module, $type = NULL, $id = NULL, $count = 1) {
     // Delete rows that have a exact or less value to prevent empty rows.
-    $query = db_delete('file_usage')
+    $query = $this->connection->delete('file_usage')
       ->condition('module', $module)
       ->condition('fid', $file->fid);
     if ($type && $id) {
@@ -53,7 +67,7 @@
 
     // If the row has more than the specified count decrement it by that number.
     if (!$result && $count > 0) {
-      $query = db_update('file_usage')
+      $query = $this->connection->update('file_usage')
         ->condition('module', $module)
         ->condition('fid', $file->fid);
       if ($type && $id) {
@@ -69,10 +83,10 @@
   }
 
   /**
-   * Implements Drupal\Core\FileUsage\FileUsageInterface::list_usage().
+   * Implements Drupal\Core\FileUsage\FileUsageInterface::listUsage().
    */
-  function list_usage(File $file) {
-    $result = db_select('file_usage', 'f')
+  public function listUsage(File $file) {
+    $result = $this->connection->select('file_usage', 'f')
       ->fields('f', array('module', 'type', 'id', 'count'))
       ->condition('fid', $file->fid)
       ->condition('count', 0, '>')
diff -u b/core/lib/Drupal/Core/FileUsage/FileUsageBase.php b/core/lib/Drupal/Core/FileUsage/FileUsageBase.php
--- b/core/lib/Drupal/Core/FileUsage/FileUsageBase.php
+++ b/core/lib/Drupal/Core/FileUsage/FileUsageBase.php
@@ -17,7 +17,7 @@
   /**
    * Implements Drupal\Core\FileUsage\FileUsageInterface::add().
    */
-  function add(File $file, $module, $type, $id, $count = 1) {
+  public function add(File $file, $module, $type, $id, $count = 1) {
     // Make sure that a used file is permament.
     if ($file->status != FILE_STATUS_PERMANENT) {
       $file->status = FILE_STATUS_PERMANENT;
@@ -28,10 +28,10 @@
   /**
    * Implements Drupal\Core\FileUsage\FileUsageInterface::delete().
    */
-  function delete(File $file, $module, $type = NULL, $id = NULL, $count = 1) {
+  public function delete(File $file, $module, $type = NULL, $id = NULL, $count = 1) {
     // If there are no more remaining usages of this file, mark it as temporary,
     // which result in a delete through system_cron().
-    $usage = file_usage()->list_usage($file);
+    $usage = file_usage()->listUsage($file);
     if (empty($usage)) {
       $file->status = 0;
       $file->save();
diff -u b/core/lib/Drupal/Core/FileUsage/FileUsageInterface.php b/core/lib/Drupal/Core/FileUsage/FileUsageInterface.php
--- b/core/lib/Drupal/Core/FileUsage/FileUsageInterface.php
+++ b/core/lib/Drupal/Core/FileUsage/FileUsageInterface.php
@@ -70,3 +70,3 @@
    */
-  public function list_usage(File $file);
+  public function listUsage(File $file);
 }
diff -u b/core/modules/file/file.module b/core/modules/file/file.module
--- b/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -298,7 +298,7 @@
     module_invoke_all('file_move', $file, $source);
 
     // Delete the original if it's not in use elsewhere.
-    if ($delete_source && !file_usage()->list_usage($source)) {
+    if ($delete_source && !file_usage()->listUsage($source)) {
       $source->delete();
     }
 
@@ -758,7 +758,7 @@
   ));
   foreach ($result as $row) {
     if ($file = file_load($row->fid)) {
-      $references = file_usage()->list_usage($file);
+      $references = file_usage()->listUsage($file);
       if (empty($references)) {
         if (file_exists($file->uri)) {
           $file->delete();
@@ -1111,7 +1111,7 @@
   if ($clicked_button != 'remove_button' && !empty($element['fid']['#value'])) {
     if ($file = file_load($element['fid']['#value'])) {
       if ($file->status == FILE_STATUS_PERMANENT) {
-        $references = file_usage()->list_usage($file);
+        $references = file_usage()->listUsage($file);
         if (empty($references)) {
           form_error($element, t('The file used in the !name field may not be referenced.', array('!name' => $element['#title'])));
         }
diff -u b/core/modules/file/lib/Drupal/file/Tests/DeleteTest.php b/core/modules/file/lib/Drupal/file/Tests/DeleteTest.php
--- b/core/modules/file/lib/Drupal/file/Tests/DeleteTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/DeleteTest.php
@@ -42,7 +42,7 @@
     file_usage()->add($file, 'testing', 'test', 1);
 
     file_usage()->delete($file, 'testing', 'test', 1);
-    $usage = file_usage()->list_usage($file);
+    $usage = file_usage()->listUsage($file);
     $this->assertEqual($usage['testing']['test'], array(1 => 1), t('Test file is still in use.'));
     $this->assertTrue(file_exists($file->uri), t('File still exists on the disk.'));
     $this->assertTrue(file_load($file->fid), t('File still exists in the database.'));
@@ -51,7 +51,7 @@
     file_test_reset();
 
     file_usage()->delete($file, 'testing', 'test', 1);
-    $usage = file_usage()->list_usage($file);
+    $usage = file_usage()->listUsage($file);
     $this->assertFileHooksCalled(array('load', 'update'));
     $this->assertTrue(empty($usage), t('File usage data was removed.'));
     $this->assertTrue(file_exists($file->uri), 'File still exists on the disk.');
diff -u b/core/modules/file/lib/Drupal/file/Tests/UsageTest.php b/core/modules/file/lib/Drupal/file/Tests/UsageTest.php
--- b/core/modules/file/lib/Drupal/file/Tests/UsageTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/UsageTest.php
@@ -20,7 +20,7 @@
   }
 
   /**
-   * Tests file_usage()->list_usage().
+   * Tests file_usage()->listUsage().
    */
   function testGetUsage() {
     $file = $this->createFile();
@@ -43,7 +43,7 @@
       ))
       ->execute();
 
-    $usage = file_usage()->list_usage($file);
+    $usage = file_usage()->listUsage($file);
 
     $this->assertEqual(count($usage['testing']), 2, t('Returned the correct number of items.'));
     $this->assertTrue(isset($usage['testing']['foo'][1]), t('Returned the correct id.'));
diff -u b/core/modules/system/tests/modules/bundle_test/lib/Drupal/bundle_test/TestFileUsage.php b/core/modules/system/tests/modules/bundle_test/lib/Drupal/bundle_test/TestFileUsage.php
--- b/core/modules/system/tests/modules/bundle_test/lib/Drupal/bundle_test/TestFileUsage.php
+++ b/core/modules/system/tests/modules/bundle_test/lib/Drupal/bundle_test/TestFileUsage.php
@@ -15,17 +15,17 @@
    * Implements Drupal\Core\FileUsage\FileUsageInterface::add().
    */
-  function add(File $file, $module, $type, $id, $count = 1) {
+  public function add(File $file, $module, $type, $id, $count = 1) {
   }
 
   /**
    * Implements Drupal\Core\FileUsage\FileUsageInterface::delete().
    */
-  function delete(File $file, $module, $type = NULL, $id = NULL, $count = 1) {
+  public function delete(File $file, $module, $type = NULL, $id = NULL, $count = 1) {
   }
 
   /**
-   * Implements Drupal\Core\FileUsage\FileUsageInterface::list_usage().
+   * Implements Drupal\Core\FileUsage\FileUsageInterface::listUsage().
    */
-  function list_usage(File $file) {
+  public function listUsage(File $file) {
   }
 }