Revert "Make common page base class for XFA and non-XFA."

This reverts commit d06cc38b76685b002c51b227ae43b8314d926ad8.

Reason for revert: blocking previous revert

Change-Id: I74f8b80852c671440cca5fabef30e69cde9e2063
Reviewed-on: https://pdfium-review.googlesource.com/33713
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
diff --git a/fpdfsdk/cpdfsdk_interform.cpp b/fpdfsdk/cpdfsdk_interform.cpp
index 3b92723..638b4df 100644
--- a/fpdfsdk/cpdfsdk_interform.cpp
+++ b/fpdfsdk/cpdfsdk_interform.cpp
@@ -361,7 +361,7 @@
     if (!pWidget)
       continue;
 
-    IPDF_Page* pPage = pWidget->GetPage();
+    UnderlyingPageType* pPage = pWidget->GetUnderlyingPage();
     FX_RECT rect = formfiller->GetViewBBox(
         m_pFormFillEnv->GetPageView(pPage, false), pWidget);
     m_pFormFillEnv->Invalidate(pPage, rect);