Import web-platform-tests media/ directory.

Many media-related tests in web-platform-tests depend on it.
https://github.com/w3c/web-platform-tests/tree/master/media

This CL has no behavior changes.

TBR=kojii@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/2401833002 .

Cr-Commit-Position: refs/heads/master@{#423793}

third_party/WebKit/LayoutTests/W3CImportExpectations

@@ -252,7 +252,8 @@ imported/wpt/js [ Skip ]
 imported/wpt/lint [ Skip ]
 imported/wpt/lint.whitelist [ Skip ]
 imported/wpt/manifest [ Skip ]
-imported/wpt/media [ Skip ]
+## Owners: none; No tests in the directory.
+# imported/wpt/media [ Skip ]
 imported/wpt/media-source [ Skip ]
 ## Owners: phoglund@chromium.org
 # imported/wpt/mediacapture-streams [ Pass ]

third_party/WebKit/LayoutTests/imported/wpt/media/foo.vtt

+WEBVTT
+
+00:00:00.000 --> 00:00:05.000
+Foo

third_party/WebKit/LayoutTests/imported/wpt/media/foo.vtt.headers

+Access-Control-Allow-Origin: *
\ No newline at end of file