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

Source/core/html/canvas/WebGLContextEvent.h

Index: Source/core/html/canvas/WebGLContextEvent.h
diff --git a/Source/core/html/canvas/WebGLContextEvent.h b/Source/core/html/canvas/WebGLContextEvent.h
index e8028a2a6c1c0a0c08406bc413f414ed59a69bb2..85c97d8ab407a3370dbdaf78aea0db25bcb8454e 100644
--- a/Source/core/html/canvas/WebGLContextEvent.h
+++ b/Source/core/html/canvas/WebGLContextEvent.h
@@ -27,15 +27,10 @@
 #define WebGLContextEvent_h
 
 #include "core/events/Event.h"
+#include "core/html/canvas/WebGLContextEventInit.h"
 
 namespace blink {
 
-struct WebGLContextEventInit : public EventInit {
-    WebGLContextEventInit();
-
-    String statusMessage;
-};
-
 class WebGLContextEvent final : public Event {
     DEFINE_WRAPPERTYPEINFO();