Use some CFX_DIBBase methods directly in CStretchEngine.

Use existing CFX_DIBBase helper methods, rather than reimplementing
them.

Change-Id: I2398fee65c8a92edbf51ffe3ffb9f4522706a2db
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/90850
Reviewed-by: Nigi <nigi@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/core/fxge/dib/cstretchengine.cpp b/core/fxge/dib/cstretchengine.cpp
index 361edf4..8fbd0c8 100644
--- a/core/fxge/dib/cstretchengine.cpp
+++ b/core/fxge/dib/cstretchengine.cpp
@@ -177,8 +177,8 @@
                                const FXDIB_ResampleOptions& options)
     : m_DestFormat(dest_format),
       m_DestBpp(GetBppFromFormat(dest_format)),
-      m_SrcBpp(GetBppFromFormat(pSrcBitmap->GetFormat())),
-      m_bHasAlpha(GetIsAlphaFromFormat(pSrcBitmap->GetFormat())),
+      m_SrcBpp(pSrcBitmap->GetBPP()),
+      m_bHasAlpha(pSrcBitmap->IsAlphaFormat()),
       m_pSource(pSrcBitmap),
       m_pSrcPalette(pSrcBitmap->GetPaletteSpan()),
       m_SrcWidth(pSrcBitmap->GetWidth()),