The final game: mark everything final.

Then revert the ones that break compilation.
Fix one IWYU noticed during presubmit.

Change-Id: I881a8a72818e55dbc4816247e35ff5e3015194e7
Reviewed-on: https://pdfium-review.googlesource.com/41470
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
diff --git a/fxjs/cjs_event.h b/fxjs/cjs_event.h
index 67bd3f5..a6308ec 100644
--- a/fxjs/cjs_event.h
+++ b/fxjs/cjs_event.h
@@ -9,7 +9,7 @@
 
 #include "fxjs/js_define.h"
 
-class CJS_Event : public CJS_Object {
+class CJS_Event final : public CJS_Object {
  public:
   static int GetObjDefnID();
   static void DefineJSObjects(CFXJS_Engine* pEngine);