Change DrawAppearance() methods to take CFX_Matrix by const-ref.

Change-Id: If038850c745ac26e50c313bdbe630483434caedc
Reviewed-on: https://pdfium-review.googlesource.com/11390
Commit-Queue: dsinclair <dsinclair@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
diff --git a/fpdfsdk/cpdfsdk_widget.h b/fpdfsdk/cpdfsdk_widget.h
index 954369d..5c63400 100644
--- a/fpdfsdk/cpdfsdk_widget.h
+++ b/fpdfsdk/cpdfsdk_widget.h
@@ -135,7 +135,7 @@
 
   bool IsWidgetAppearanceValid(CPDF_Annot::AppearanceMode mode);
   void DrawAppearance(CFX_RenderDevice* pDevice,
-                      const CFX_Matrix* pUser2Device,
+                      const CFX_Matrix& mtUser2Device,
                       CPDF_Annot::AppearanceMode mode,
                       const CPDF_RenderOptions* pOptions) override;