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/fxbarcode/cbc_qrcode.h b/fxbarcode/cbc_qrcode.h
index 509de8a..59d57ac 100644
--- a/fxbarcode/cbc_qrcode.h
+++ b/fxbarcode/cbc_qrcode.h
@@ -14,7 +14,7 @@
 
 class CBC_QRCodeWriter;
 
-class CBC_QRCode : public CBC_CodeBase {
+class CBC_QRCode final : public CBC_CodeBase {
  public:
   CBC_QRCode();
   ~CBC_QRCode() override;