MAGETWO-63987: Remove uses of unserialize in \Magento\Sales\Model\Order\Creditmemo\Item attribute tax_ratio

- fixed static tests

Author: vgoncharenko

dev/tests/static/testsuite/Magento/Test/Integrity/HhvmCompatibilityTest.php

@@ -37,7 +37,14 @@ class HhvmCompatibilityTest extends \PHPUnit_Framework_TestCase
         'display_errors',
         'default_socket_timeout',
         'pcre.recursion_limit',
-        'default_charset'
+        'default_charset',
+
+        /*
+          There is not way to specify calculation/serialization precision in hhvm.
+          Adding to whitelist in order to align precisions in php.
+        */
+        'precision',
+        'serialize_precision',
     ];
 
     public function testAllowedIniGetSetDirectives()