Cleanup FWL Event and Message code.

xfa/fwl/core/cfwl_message.h

Index: xfa/fwl/core/cfwl_message.h
diff --git a/xfa/fwl/core/cfwl_message.h b/xfa/fwl/core/cfwl_message.h
index 827b4181e35c7788a6d7581ec5eb1d3f9b4b2a7a..8028bf6cbb03db8f5f76499c315ea56795a16db7 100644
--- a/xfa/fwl/core/cfwl_message.h
+++ b/xfa/fwl/core/cfwl_message.h
@@ -15,7 +15,6 @@
 #include "xfa/fwl/core/fwl_error.h"
 
 enum class CFWL_MessageType {
-  None = 0,
   Key,
   KillFocus,
   Mouse,
@@ -27,15 +26,18 @@ class CFWL_Widget;
 
 class CFWL_Message {
  public:
-  CFWL_Message();
+  explicit CFWL_Message(CFWL_MessageType type);
   virtual ~CFWL_Message();
 
   virtual std::unique_ptr<CFWL_Message> Clone();
-  virtual CFWL_MessageType GetClassID() const;
+  CFWL_MessageType GetClassID() const { return m_type; }
 
   CFWL_Widget* m_pSrcTarget;
   CFWL_Widget* m_pDstTarget;
   uint32_t m_dwExtend;
+
+ private:
+  CFWL_MessageType m_type;
 };