Base: Make base::File use ScopedFD on POSIX.

base/files/file_win.cc

Index: base/files/file_win.cc
diff --git a/base/files/file_win.cc b/base/files/file_win.cc
index 2bd69c7955595fec5ab9036a17f84e8cf9ed8c1c..1e13381e255f00be678f0c224b933b729bd47ab8 100644
--- a/base/files/file_win.cc
+++ b/base/files/file_win.cc
@@ -99,6 +99,11 @@ void File::InitializeUnsafe(const FilePath& name, uint32 flags) {
 bool File::IsValid() const {
   return file_.IsValid();
 }
+
+PlatformFile File::GetPlatformFile() const {
+  return file_;
+}
+
 PlatformFile File::TakePlatformFile() {
   return file_.Take();
 }