Cleanup FWL Event and Message code.

xfa/fwl/core/cfwl_msgmouse.cpp

Index: xfa/fwl/core/cfwl_msgmouse.cpp
diff --git a/xfa/fwl/core/cfwl_msgmouse.cpp b/xfa/fwl/core/cfwl_msgmouse.cpp
index de2540d8fc881cc294392154150595907f81a27d..dc62cd60306a45abc4fb74b5174bdca20dda7403 100644
--- a/xfa/fwl/core/cfwl_msgmouse.cpp
+++ b/xfa/fwl/core/cfwl_msgmouse.cpp
@@ -10,14 +10,10 @@
 
 #include "third_party/base/ptr_util.h"
 
-CFWL_MsgMouse::CFWL_MsgMouse() {}
+CFWL_MsgMouse::CFWL_MsgMouse() : CFWL_Message(CFWL_MessageType::Mouse) {}
 
 CFWL_MsgMouse::~CFWL_MsgMouse() {}
 
 std::unique_ptr<CFWL_Message> CFWL_MsgMouse::Clone() {
   return pdfium::MakeUnique<CFWL_MsgMouse>(*this);
 }
-
-CFWL_MessageType CFWL_MsgMouse::GetClassID() const {
-  return CFWL_MessageType::Mouse;
-}