Fix an unused variable warning in release builds.

Bug: chromium:1203071
Change-Id: If2cab8dc33b126a4dd73b57c7e8a35311ea685ce
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/86071
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
diff --git a/core/fxge/win32/cfx_psfonttracker.cpp b/core/fxge/win32/cfx_psfonttracker.cpp
index d6a5240..9e7ec57 100644
--- a/core/fxge/win32/cfx_psfonttracker.cpp
+++ b/core/fxge/win32/cfx_psfonttracker.cpp
@@ -6,6 +6,7 @@
 
 #include "core/fxge/cfx_font.h"
 #include "third_party/base/check.h"
+#include "third_party/base/compiler_specific.h"
 #include "third_party/base/containers/contains.h"
 
 CFX_PSFontTracker::CFX_PSFontTracker() = default;
@@ -21,6 +22,7 @@
     inserted = seen_font_ptrs_.insert(UnownedPtr<const CFX_Font>(font)).second;
   }
   DCHECK(inserted);
+  ALLOW_UNUSED_LOCAL(inserted);
 }
 
 bool CFX_PSFontTracker::SeenFontObject(const CFX_Font* font) const {