Add LayoutTests for mixed range response handling.

LayoutTests/http/tests/media/resources/mixed-range-response.php

Index: LayoutTests/http/tests/media/resources/mixed-range-response.php
diff --git a/LayoutTests/http/tests/media/resources/mixed-range-response.php b/LayoutTests/http/tests/media/resources/mixed-range-response.php
new file mode 100644
index 0000000000000000000000000000000000000000..6f52d4959f22675a13e605d7b7f3e2027a84183b
--- /dev/null
+++ b/LayoutTests/http/tests/media/resources/mixed-range-response.php
@@ -0,0 +1,12 @@
+<?php
+if (isset($_SERVER['HTTP_RANGE']) && ($_SERVER['HTTP_RANGE'] == 'bytes=0-')) {
+  header('HTTP/1.0 206 Partial Content');
+  header('Content-Type: audio/ogg');
+  header('Content-Range: bytes 0-3/12983');
+  echo 'Ogg';
+  return;
+}
+header('HTTP/1.1 307 Temporary Redirect');
+header('Location: http://127.0.0.1:8000/media/resources/load-video.php?' .
+       'name=../../../../media/content/silence.oga&type=audio/ogg');
+?>