Split the common event classes out to files.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 7b634a7e8af6279034265041c67b724659c0d4c5..d7cab2d3a3b8877d913915b4d635c0ddc6cb8df0 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1178,7 +1178,26 @@ if (pdf_enable_xfa) {
       "xfa/fwl/core/cfwl_datetimepicker.h",
       "xfa/fwl/core/cfwl_edit.cpp",
       "xfa/fwl/core/cfwl_edit.h",
+      "xfa/fwl/core/cfwl_event.cpp",
       "xfa/fwl/core/cfwl_event.h",
+      "xfa/fwl/core/cfwl_evtclick.cpp",
+      "xfa/fwl/core/cfwl_evtclick.h",
+      "xfa/fwl/core/cfwl_evtclose.cpp",
+      "xfa/fwl/core/cfwl_evtclose.h",
+      "xfa/fwl/core/cfwl_evtkey.cpp",
+      "xfa/fwl/core/cfwl_evtkey.h",
+      "xfa/fwl/core/cfwl_evtkillfocus.cpp",
+      "xfa/fwl/core/cfwl_evtkillfocus.h",
+      "xfa/fwl/core/cfwl_evtmouse.cpp",
+      "xfa/fwl/core/cfwl_evtmouse.h",
+      "xfa/fwl/core/cfwl_evtmousewheel.cpp",
+      "xfa/fwl/core/cfwl_evtmousewheel.h",
+      "xfa/fwl/core/cfwl_evtscroll.cpp",
+      "xfa/fwl/core/cfwl_evtscroll.h",
+      "xfa/fwl/core/cfwl_evtsetfocus.cpp",
+      "xfa/fwl/core/cfwl_evtsetfocus.h",
+      "xfa/fwl/core/cfwl_evtsizechanged.cpp",
+      "xfa/fwl/core/cfwl_evtsizechanged.h",
       "xfa/fwl/core/cfwl_listbox.cpp",
       "xfa/fwl/core/cfwl_listbox.h",
       "xfa/fwl/core/cfwl_listitem.cpp",