Implement Blob.close().

LayoutTests/http/tests/xmlhttprequest/resources/multipart-post-echo.php

Index: LayoutTests/http/tests/xmlhttprequest/resources/multipart-post-echo.php
diff --git a/LayoutTests/http/tests/xmlhttprequest/resources/multipart-post-echo.php b/LayoutTests/http/tests/xmlhttprequest/resources/multipart-post-echo.php
index 9e7281b11b47b98f1fe9667e6607d74953628690..4b0ac105a22b8a621a43057eff0e7cbe7c8f9236 100644
--- a/LayoutTests/http/tests/xmlhttprequest/resources/multipart-post-echo.php
+++ b/LayoutTests/http/tests/xmlhttprequest/resources/multipart-post-echo.php
@@ -18,7 +18,7 @@ foreach ($_FILES as $key => $value) {
     } else {
         $fp = fopen($file['tmp_name'], 'r');
         if ($fp) {
-            $content = fread($fp, $file['size']);
+            $content = $file['size'] > 0 ? fread($fp, $file['size']) : "";
             fclose($fp);
         }
         $values[] = $key . '=' . $file['name'] . ':' . $file['type'] . ':' . $content;