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

Source/core/css/MediaQueryListEvent.h

Index: Source/core/css/MediaQueryListEvent.h
diff --git a/Source/core/css/MediaQueryListEvent.h b/Source/core/css/MediaQueryListEvent.h
index f5786bf246142f13e0829633ac2c0f5f610d83cd..ed185059cf95d5d8af7aee734f5cc48e08f3e5b8 100644
--- a/Source/core/css/MediaQueryListEvent.h
+++ b/Source/core/css/MediaQueryListEvent.h
@@ -6,17 +6,11 @@
 #define MediaQueryListEvent_h
 
 #include "core/css/MediaQueryList.h"
+#include "core/css/MediaQueryListEventInit.h"
 #include "core/events/Event.h"
 
 namespace blink {
 
-struct MediaQueryListEventInit : public EventInit {
-    MediaQueryListEventInit() : matches(false) { }
-
-    String media;
-    bool matches;
-};
-
 class MediaQueryListEvent final : public Event {
     DEFINE_WRAPPERTYPEINFO();
 public:
@@ -67,8 +61,13 @@ private:
 
     MediaQueryListEvent(const AtomicString& eventType, const MediaQueryListEventInit& initializer)
         : Event(eventType, initializer)
-        , m_media(initializer.media)
-        , m_matches(initializer.matches) { }
+        , m_matches(false)
+    {
+        if (initializer.hasMedia())
+            m_media = initializer.media();
+        if (initializer.hasMatches())
+            m_matches = initializer.matches();
+    }
 
     // We have m_media/m_matches for JS-created events; we use m_mediaQueryList
     // for events that blink generates.