Use event init dictionaries in core/{css,html}

Source/core/html/MediaKeyEventInit.idl

Index: Source/core/html/MediaKeyEventInit.idl
diff --git a/Source/core/html/MediaKeyEventInit.idl b/Source/core/html/MediaKeyEventInit.idl
new file mode 100644
index 0000000000000000000000000000000000000000..b8eb75a744e86f964a2526fb33ec15ea966aade6
--- /dev/null
+++ b/Source/core/html/MediaKeyEventInit.idl
@@ -0,0 +1,13 @@
+// Copyright 2014 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.
+
+dictionary MediaKeyEventInit : EventInit {
+    DOMString keySystem;
+    DOMString sessionId;
+    Uint8Array initData;
+    Uint8Array message;
+    DOMString defaultURL;
+    MediaKeyError? errorCode;
+    unsigned short systemCode;
+};