MC-31362: Media folder update

- Corrected variable scope

Author: Hwashiang Yu

app/code/Magento/Theme/Model/Design/Backend/File.php

@@ -39,12 +39,12 @@ class File extends BackendFile
     /**
      * @var Mime
      */
-    protected $mime;
+    private $mime;
 
     /**
      * @var IoFileSystem
      */
-    protected $ioFileSystem;
+    private $ioFileSystem;
 
     /**
      * @var Database

app/code/Magento/Theme/Test/Unit/Model/Design/Backend/FileTest.php

@@ -25,7 +25,7 @@ class FileTest extends \PHPUnit\Framework\TestCase
     protected $fileBackend;
 
     /** @var IoFileSystem|\PHPUnit_Framework_MockObject_MockObject */
-    protected $ioFileSystem;
+    private $ioFileSystem;
 
     /**
      * @var \Magento\Framework\File\Mime|\PHPUnit_Framework_MockObject_MockObject

app/code/Magento/Theme/Test/Unit/Model/Design/Backend/ImageTest.php

@@ -25,7 +25,7 @@ class ImageTest extends \PHPUnit\Framework\TestCase
     protected $imageBackend;
 
     /** @var IoFileSystem|\PHPUnit_Framework_MockObject_MockObject */
-    protected $ioFileSystem;
+    private $ioFileSystem;
 
     /**
      * @var \Magento\Framework\File\Mime|\PHPUnit_Framework_MockObject_MockObject
@@ -93,13 +93,6 @@ public function setUp()
             $this->databaseHelper,
             $this->ioFileSystem
         );
-
-        $objectManager = new \Magento\Framework\TestFramework\Unit\Helper\ObjectManager($this);
-        $objectManager->setBackwardCompatibleProperty(
-            $this->imageBackend,
-            'mime',
-            $this->mime
-        );
     }
 
     public function tearDown()