Make CPDF_Object subclass constructors intern strings

core/fpdfapi/parser/cpdf_object.h

Index: core/fpdfapi/parser/cpdf_object.h
diff --git a/core/fpdfapi/parser/cpdf_object.h b/core/fpdfapi/parser/cpdf_object.h
index c24b40a7896808885533b0d3bceff587907fee22..9c41e9de7b4af1fb5640b141eb5763c70106e793 100644
--- a/core/fpdfapi/parser/cpdf_object.h
+++ b/core/fpdfapi/parser/cpdf_object.h
@@ -9,6 +9,7 @@
 
 #include <memory>
 #include <set>
+#include <type_traits>
 
 #include "core/fxcrt/fx_string.h"
 #include "core/fxcrt/fx_system.h"
@@ -117,4 +118,12 @@ class CPDF_Object {
   CPDF_Object(const CPDF_Object& src) {}
 };
 
+template <typename T>
+struct CanInternStrings {
+  static const bool value = std::is_same<T, CPDF_Array>::value ||
+                            std::is_same<T, CPDF_Dictionary>::value ||
+                            std::is_same<T, CPDF_Name>::value ||
+                            std::is_same<T, CPDF_String>::value;
+};
+
 #endif  // CORE_FPDFAPI_PARSER_CPDF_OBJECT_H_