Add ptr_util.h from base until std::make_unique<> available

fpdfsdk/javascript/JS_Runtime_Stub.cpp

Index: fpdfsdk/javascript/JS_Runtime_Stub.cpp
diff --git a/fpdfsdk/javascript/JS_Runtime_Stub.cpp b/fpdfsdk/javascript/JS_Runtime_Stub.cpp
index 3b316aaf699dcfa411062af3f15402391dbc9742..8d8ac33474822fe5e9627c97c5afe278e5838462 100644
--- a/fpdfsdk/javascript/JS_Runtime_Stub.cpp
+++ b/fpdfsdk/javascript/JS_Runtime_Stub.cpp
@@ -8,6 +8,7 @@
 
 #include "fpdfsdk/javascript/ijs_context.h"
 #include "fpdfsdk/javascript/ijs_runtime.h"
+#include "third_party/base/ptr_util.h"
 
 class CJS_ContextStub final : public IJS_Context {
  public:
@@ -124,7 +125,7 @@ class CJS_RuntimeStub final : public IJS_Runtime {
 
   IJS_Context* NewContext() override {
     if (!m_pContext)
-      m_pContext = WrapUnique(new CJS_ContextStub());
+      m_pContext = pdfium::MakeUnique<CJS_ContextStub>();
     return GetCurrentContext();
   }