Convert single use EventTypes to class files.

xfa/fwl/core/cfwl_evtpostdropdown.h

Index: xfa/fwl/core/cfwl_evtpostdropdown.h
diff --git a/xfa/fwl/core/cfwl_evtclick.h b/xfa/fwl/core/cfwl_evtpostdropdown.h
similarity index 57%
copy from xfa/fwl/core/cfwl_evtclick.h
copy to xfa/fwl/core/cfwl_evtpostdropdown.h
index 280004a6e9ff9567fad1fbd8297f8d06446b4662..b4d85165937ff84f393900234fe9bc4ad45031e2 100644
--- a/xfa/fwl/core/cfwl_evtclick.h
+++ b/xfa/fwl/core/cfwl_evtpostdropdown.h
@@ -4,17 +4,17 @@
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
-#ifndef XFA_FWL_CORE_CFWL_EVTCLICK_H_
-#define XFA_FWL_CORE_CFWL_EVTCLICK_H_
+#ifndef XFA_FWL_CORE_CFWL_EVTPOSTDROPDOWN_H_
+#define XFA_FWL_CORE_CFWL_EVTPOSTDROPDOWN_H_
 
 #include "xfa/fwl/core/cfwl_event.h"
 
-class CFWL_EvtClick : public CFWL_Event {
+class CFWL_EvtPostDropDown : public CFWL_Event {
  public:
-  CFWL_EvtClick();
-  ~CFWL_EvtClick() override;
+  CFWL_EvtPostDropDown();
+  ~CFWL_EvtPostDropDown() override;
 
   CFWL_EventType GetClassID() const override;
 };
 
-#endif  // XFA_FWL_CORE_CFWL_EVTCLICK_H_
+#endif  // XFA_FWL_CORE_CFWL_EVTPOSTDROPDOWN_H_