Fix build for when pdf_use_win32_gdi=true.

Add a missing include.

Change-Id: I8965c611ba179ee04166662f4ee4a3a26653d38c
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/83170
Auto-Submit: Lei Zhang <thestig@chromium.org>
Commit-Queue: Hui Yingst <nigi@chromium.org>
Reviewed-by: Hui Yingst <nigi@chromium.org>
diff --git a/core/fxge/win32/cgdi_printer_driver.cpp b/core/fxge/win32/cgdi_printer_driver.cpp
index 51b1646..a234014 100644
--- a/core/fxge/win32/cgdi_printer_driver.cpp
+++ b/core/fxge/win32/cgdi_printer_driver.cpp
@@ -25,6 +25,10 @@
 #include "third_party/base/check_op.h"
 
 #if defined(PDFIUM_PRINT_TEXT_WITH_GDI)
+#include "core/fxcrt/widestring.h"
+#endif
+
+#if defined(PDFIUM_PRINT_TEXT_WITH_GDI)
 namespace {
 
 class ScopedState {