Mark CFX_RenderDevice::SetBitmap() as protected

Only let sub-classes initialize the bitmap.

Change-Id: If064d6168d8a90a74b97a987b6d33346ed623c55
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/115390
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
diff --git a/core/fxge/cfx_renderdevice.h b/core/fxge/cfx_renderdevice.h
index 81d8d2b..8295a06 100644
--- a/core/fxge/cfx_renderdevice.h
+++ b/core/fxge/cfx_renderdevice.h
@@ -63,7 +63,6 @@
   int GetRenderCaps() const { return m_RenderCaps; }
   int GetDeviceCaps(int id) const;
   RetainPtr<CFX_DIBitmap> GetBitmap() const;
-  void SetBitmap(const RetainPtr<CFX_DIBitmap>& pBitmap);
   [[nodiscard]] bool CreateCompatibleBitmap(const RetainPtr<CFX_DIBitmap>& pDIB,
                                             int width,
                                             int height) const;
@@ -227,6 +226,8 @@
  protected:
   CFX_RenderDevice();
 
+  void SetBitmap(const RetainPtr<CFX_DIBitmap>& pBitmap);
+
   void SetDeviceDriver(std::unique_ptr<RenderDeviceDriverIface> pDriver);
   RenderDeviceDriverIface* GetDeviceDriver() const {
     return m_pDeviceDriver.get();