[Locale][Testing] Fixed breaking tests if 'intl' extension is not installed (#3139)

Symfony\Tests\Component\Locale\LocaleTest->testGetDisplayCountriesReturnsFullListForSubLocale()
fails with a fatal error if the PHP extension 'intl' is not installed on the system.
Added a check which skips the affected tests if the extension is not available.
Fixes #3139

tests/Symfony/Tests/Component/Locale/LocaleTest.php

@@ -11,12 +11,16 @@
 
 namespace Symfony\Tests\Component\Locale;
 
+require_once __DIR__.'/TestCase.php';
+
 use Symfony\Component\Locale\Locale;
+use Symfony\Tests\Component\Locale\TestCase as LocaleTestCase;
 
-class LocaleTest extends \PHPUnit_Framework_TestCase
+class LocaleTest extends LocaleTestCase
 {
     public function testGetDisplayCountriesReturnsFullListForSubLocale()
     {
+        $this->skipIfIntlExtensionIsNotLoaded();
         $countriesDe = Locale::getDisplayCountries('de');
         $countriesDeCh = Locale::getDisplayCountries('de_CH');
 
@@ -27,6 +31,7 @@ class LocaleTest extends \PHPUnit_Framework_TestCase
 
     public function testGetDisplayLanguagesReturnsFullListForSubLocale()
     {
+        $this->skipIfIntlExtensionIsNotLoaded();
         $languagesDe = Locale::getDisplayLanguages('de');
         $languagesDeCh = Locale::getDisplayLanguages('de_CH');
 
@@ -37,6 +42,7 @@ class LocaleTest extends \PHPUnit_Framework_TestCase
 
     public function testGetDisplayLocalesReturnsFullListForSubLocale()
     {
+        $this->skipIfIntlExtensionIsNotLoaded();
         $localesDe = Locale::getDisplayLocales('de');
         $localesDeCh = Locale::getDisplayLocales('de_CH');