Add missing include for C++23

unique_ptr<T> needs T to be defined.

Bug: 388070065
Change-Id: Ifb6c7f22cf0b8042fec1d79253d4a7a0731f2487
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/136210
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Auto-Submit: David Benjamin <davidben@google.com>
diff --git a/core/fxcodec/jbig2/JBig2_SymbolDict.h b/core/fxcodec/jbig2/JBig2_SymbolDict.h
index 5a65d28..dfa694f 100644
--- a/core/fxcodec/jbig2/JBig2_SymbolDict.h
+++ b/core/fxcodec/jbig2/JBig2_SymbolDict.h
@@ -12,8 +12,7 @@
 #include <vector>
 
 #include "core/fxcodec/jbig2/JBig2_ArithDecoder.h"
-
-class CJBig2_Image;
+#include "core/fxcodec/jbig2/JBig2_Image.h"
 
 class CJBig2_SymbolDict {
  public: