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

Source/core/html/MediaKeyEvent.idl

Index: Source/core/html/MediaKeyEvent.idl
diff --git a/Source/core/html/MediaKeyEvent.idl b/Source/core/html/MediaKeyEvent.idl
index ec80808d74529ecfb822df60892a2f70884432a2..1159db09b39f515a5f10adaf53b28d622a79d560 100644
--- a/Source/core/html/MediaKeyEvent.idl
+++ b/Source/core/html/MediaKeyEvent.idl
@@ -24,15 +24,15 @@
  */
 
 [
-    EventConstructor,
+    Constructor(DOMString type, optional MediaKeyEventInit eventInitDict),
     RuntimeEnabled=PrefixedEncryptedMedia,
 ] interface MediaKeyEvent : Event {
-    [InitializedByEventConstructor] readonly attribute DOMString keySystem;
-    [InitializedByEventConstructor] readonly attribute DOMString sessionId;
-    [InitializedByEventConstructor] readonly attribute Uint8Array initData;
-    [InitializedByEventConstructor] readonly attribute Uint8Array message;
-    [InitializedByEventConstructor] readonly attribute DOMString defaultURL;
-    [InitializedByEventConstructor] readonly attribute MediaKeyError? errorCode;
-    [InitializedByEventConstructor] readonly attribute unsigned short systemCode;
+    readonly attribute DOMString keySystem;
+    readonly attribute DOMString sessionId;
+    readonly attribute Uint8Array initData;
+    readonly attribute Uint8Array message;
+    readonly attribute DOMString defaultURL;
+    readonly attribute MediaKeyError? errorCode;
+    readonly attribute unsigned short systemCode;
 };