MAGETWO-57656: Base url should be processed while sending email

Author: Karpenko, Oleksandr

app/code/Magento/Email/Model/Template/Filter.php

@@ -928,7 +928,7 @@ public function getCssFilesContent(array $files)
         try {
             foreach ($files as $file) {
                 $asset = $this->_assetRepo->createAsset($file, $designParams);
-                $filePath = $asset->getContext()->getPath() . '/' . $file;
+                $filePath = $asset->getContext()->getPath() . DIRECTORY_SEPARATOR . $file;
                 if ($this->getPubDirectory()->isExist($filePath)) {
                     $css .= $this->getPubDirectory()->readFile($filePath);
                 } else {

app/code/Magento/Email/Test/Unit/Model/Template/FilterTest.php

@@ -320,11 +320,11 @@ public function testGetCssFilesContent()
         $reflectionProperty->setValue($filter, $pubDirectory);
         $pubDirectory->expects($this->once())
             ->method('isExist')
-            ->with($path . '/' . $file)
+            ->with($path . DIRECTORY_SEPARATOR . $file)
             ->willReturn(true);
         $pubDirectory->expects($this->once())
             ->method('readFile')
-            ->with($path . '/' . $file)
+            ->with($path . DIRECTORY_SEPARATOR . $file)
             ->willReturn($css);
 
         $filter->setDesignParams($designParams);