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

third_party/BUILD.gn

Index: third_party/BUILD.gn
diff --git a/third_party/BUILD.gn b/third_party/BUILD.gn
index 11456b131a8c69456ab0ab0499380a6698a40013..51481dddef41e947810ad1f8d8f88ac76dc8e133 100644
--- a/third_party/BUILD.gn
+++ b/third_party/BUILD.gn
@@ -379,12 +379,10 @@ source_set("pdfium_base") {
   sources = [
     "base/logging.h",
     "base/macros.h",
-    "base/nonstd_unique_ptr.h",
     "base/numerics/safe_conversions.h",
     "base/numerics/safe_conversions_impl.h",
     "base/numerics/safe_math.h",
     "base/numerics/safe_math_impl.h",
     "base/stl_util.h",
-    "base/template_util.h",
   ]
 }