Switch from nonstd::unique_ptr to std::unique_ptr.

core/include/fpdfdoc/fpdf_doc.h

Index: core/include/fpdfdoc/fpdf_doc.h
diff --git a/core/include/fpdfdoc/fpdf_doc.h b/core/include/fpdfdoc/fpdf_doc.h
index 4712f607060b6858d43257962927d79bb1a09747..09c93d6c3ad68c8d33e40be7957c880f859a1b85 100644
--- a/core/include/fpdfdoc/fpdf_doc.h
+++ b/core/include/fpdfdoc/fpdf_doc.h
@@ -8,11 +8,11 @@
 #define CORE_INCLUDE_FPDFDOC_FPDF_DOC_H_
 
 #include <map>
+#include <memory>
 #include <vector>
 
 #include "core/include/fpdfapi/fpdf_parser.h"
 #include "core/include/fpdfapi/fpdf_render.h"
-#include "third_party/base/nonstd_unique_ptr.h"
 
 class CFieldTree;
 class CPDF_AAction;
@@ -700,7 +700,7 @@ class CPDF_InterForm : public CFX_PrivateData {
 
   std::map<const CPDF_Dictionary*, CPDF_FormControl*> m_ControlMap;
 
-  nonstd::unique_ptr<CFieldTree> m_pFieldTree;
+  std::unique_ptr<CFieldTree> m_pFieldTree;
 
   CFX_ByteString m_bsEncoding;
 
@@ -1060,7 +1060,7 @@ class CPDF_Metadata {
   const CXML_Element* GetRoot() const;
 
  private:
-  nonstd::unique_ptr<CXML_Element> m_pXmlElement;
+  std::unique_ptr<CXML_Element> m_pXmlElement;
 };
 
 class CPDF_ViewerPreferences {