Add layout tests for seeks to zero on streaming sources.

LayoutTests/http/tests/media/resources/serve-video.php

 <?php
 
     $fileName = $_GET["name"];
     $type = $_GET["type"];
 
     $fileSize = filesize($fileName);
     $start = 0;
     $end = $fileSize - 1;
     $contentRange = $_SERVER["HTTP_RANGE"];
-    if (isset($contentRange)) {
-        $range = explode("-", substr($contentRange, strlen("bytes="))); 
-        $start = intval($range[0]); 
+    if (isset($contentRange) && empty($_GET["norange"])) {
+        $range = explode("-", substr($contentRange, strlen("bytes=")));
+        $start = intval($range[0]);
         if (!empty($range[1]))
             $end = intval($range[1]);
         $httpStatus = "206 Partial Content";
     } else
         $httpStatus = "200 OK";
 
     header("Status: " . $httpStatus);
     header("HTTP/1.1 " . $httpStatus);
     header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
     header("Pragma: no-cache");
     header("Etag: " . '"' . $fileSize . "-" . filemtime($fileName) . '"');
     header("Content-Type: " . $type);
-    header("Accept-Ranges: bytes");
     header("Content-Length: " . ($end - $start) + 1);
-    if ($contentRange)
-                header("Content-Range: bytes " . $start . "-" . $end . "/" . $fileSize); 
+    if ($contentRange && empty($_GET["norange"])) {
+        header("Accept-Ranges: bytes");
+        header("Content-Range: bytes " . $start . "-" . $end . "/" . $fileSize);
+    }
     header("Connection: close");
 
     $chunkSize = 1024 * 256;
     $offset = $start;
 
     $fn = fopen($fileName, "rb");
     fseek($fn, $offset, 0);
 
     while (!feof($fn) && $offset <= $end && connection_status() == 0) {
         $readSize = min($chunkSize, ($end - $offset) + 1);
         $buffer = fread($fn, $readSize);
         print($buffer);
         flush();
         $offset += $chunkSize;
     }
     fclose($fn);
 
     exit;
 ?>