Convert pdfium::MakeUnique<> to std::make_unique<> in fxfa

Use C++14 features.

Change-Id: I6d15d529bb92f79da515da0744aeefbcf0f61eef
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/69994
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

xfa/fxfa/parser/cxfa_documentassembly.cpp

diff --git a/xfa/fxfa/parser/cxfa_documentassembly.cpp b/xfa/fxfa/parser/cxfa_documentassembly.cpp
index c6582e8..31238a6 100644
--- a/xfa/fxfa/parser/cxfa_documentassembly.cpp
+++ b/xfa/fxfa/parser/cxfa_documentassembly.cpp
@@ -6,8 +6,9 @@
 
 #include "xfa/fxfa/parser/cxfa_documentassembly.h"
 
+#include <memory>
+
 #include "fxjs/xfa/cjx_node.h"
-#include "third_party/base/ptr_util.h"
 
 namespace {
 
@@ -27,6 +28,6 @@
                 XFA_Element::DocumentAssembly,
                 {},
                 kDocumentAssemblyAttributeData,
-                pdfium::MakeUnique<CJX_Node>(this)) {}
+                std::make_unique<CJX_Node>(this)) {}
 
 CXFA_DocumentAssembly::~CXFA_DocumentAssembly() = default;