Add layout tests for seeks to zero on streaming sources.

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

Index: LayoutTests/http/tests/media/resources/serve-video.php
diff --git a/LayoutTests/http/tests/media/resources/serve-video.php b/LayoutTests/http/tests/media/resources/serve-video.php
index 55b3303f48679a7f18c082e8c035befe8116dd4c..9bfcf0289d2bd43e237cbf4b7c31524221842a57 100644
--- a/LayoutTests/http/tests/media/resources/serve-video.php
+++ b/LayoutTests/http/tests/media/resources/serve-video.php
@@ -7,9 +7,9 @@
     $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";
@@ -22,10 +22,11 @@
     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;