Rename enum CFWL_Part to CFWL_ThemePart::Part.

Also rename the enum values to kFoo and fix a lint error in
cfwl_themepart.h.

Bug: pdfium:547
Change-Id: I472970c01091f191788d585d310d55c5814679ec
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/81490
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/xfa/fwl/cfwl_picturebox.cpp b/xfa/fwl/cfwl_picturebox.cpp
index de4e2ba..c212c29 100644
--- a/xfa/fwl/cfwl_picturebox.cpp
+++ b/xfa/fwl/cfwl_picturebox.cpp
@@ -28,7 +28,7 @@
     return;
 
   if (HasBorder())
-    DrawBorder(pGraphics, CFWL_Part::Border, matrix);
+    DrawBorder(pGraphics, CFWL_ThemePart::Part::kBorder, matrix);
 }
 
 void CFWL_PictureBox::OnDrawWidget(CFGAS_GEGraphics* pGraphics,