Fix sticky keys crash when handling synthetic events without a native event.

ui/events/event.h

Index: ui/events/event.h
diff --git a/ui/events/event.h b/ui/events/event.h
index 51d73f8adf8f8eab576c2e7ac9f4c14b3ef14eb4..17cad8b301ecd1c37f2cc04c5de8845b97743507 100644
--- a/ui/events/event.h
+++ b/ui/events/event.h
@@ -416,11 +416,9 @@ class EVENTS_EXPORT MouseWheelEvent : public MouseEvent {
   template <class T>
   MouseWheelEvent(const MouseWheelEvent& model,
                   T* source,
-                  T* target,
-                  EventType type,
-                  int flags)
-      : MouseEvent(model, source, target, type, flags),
-        offset_(model.x_offset(), model.y_offset()){
+                  T* target)
+      : MouseEvent(model, source, target, model.type(), model.flags()),
+        offset_(model.x_offset(), model.y_offset()) {
   }
 
   // The amount to scroll. This is in multiples of kWheelDelta.