Media Capabilities: update Blink implementation and WPT to match latest spec changes.

third_party/WebKit/Source/modules/mediacapabilities/VideoConfiguration.idl

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // https://wicg.github.io/media-capabilities/#dictdef-videoconfiguration
 
 dictionary VideoConfiguration {
-    required DOMString type;
+    required DOMString contentType;
     required unsigned long width;
     required unsigned long height;
     required unsigned long bitrate;
     required double framerate;
 };