[filesapp] Reset files SWA page_factory_receiver_ if bound

The page_factory_receiver_ can be re-bound, due to developer activity
such as chrome inspector devtools page reloads for example.

Reset page_factory_receiver_ if it is bound, prior to re-binding.

Bug: 1113981
Change-Id: Idcb665fe8069baa2c6ae72f4a0098072da07c23c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2592239Reviewed-by: Alex Danilo <adanilo@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837402}

chromeos/components/file_manager/file_manager_ui.cc

@@ -87,8 +87,8 @@ FileManagerUI::~FileManagerUI() = default;
 
 void FileManagerUI::BindInterface(
     mojo::PendingReceiver<mojom::PageHandlerFactory> pending_receiver) {
-  DCHECK(!page_factory_receiver_.is_bound());
-
+  if (page_factory_receiver_.is_bound())
+    page_factory_receiver_.reset();
   page_factory_receiver_.Bind(std::move(pending_receiver));
 }