Use NoDestructor in PendingDialog::GetInstance()

NoDestructor should be preferred over Singleton according to the
comments in singleton.h and
https://bugs.chromium.org/p/chromium/issues/detail?id=925323.

And this *may* also relate to
https://bugs.chromium.org/p/chromium/issues/detail?id=922327

BUG=chromium:925323, chromium:922327
TEST=cq

Change-Id: Icb014d0eae9e0032a2a5ca56dcec59cf72300315
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2526643Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Honglin Yu <honglinyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825757}

chrome/browser/ui/views/select_file_dialog_extension.cc

@@ -15,7 +15,7 @@
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
-#include "base/memory/singleton.h"
+#include "base/no_destructor.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ -84,7 +84,8 @@ class PendingDialog {
 
 // static
 PendingDialog* PendingDialog::GetInstance() {
-  return base::Singleton<PendingDialog>::get();
+  static base::NoDestructor<PendingDialog> instance;
+  return instance.get();
 }
 
 void PendingDialog::Add(SelectFileDialogExtension::RoutingID id,