win: Ref-counted classes should have non-public destructors.

win8/viewer/metro_viewer_process_host.cc

Index: win8/viewer/metro_viewer_process_host.cc
diff --git a/win8/viewer/metro_viewer_process_host.cc b/win8/viewer/metro_viewer_process_host.cc
index 61a776c1206d7026add3b5db40e941a926da324b..348dfda678bbceb276a0ec1e160d5c2f7d1937d4 100644
--- a/win8/viewer/metro_viewer_process_host.cc
+++ b/win8/viewer/metro_viewer_process_host.cc
@@ -45,6 +45,9 @@ void MetroViewerProcessHost::InternalMessageFilter::OnChannelConnected(
   owner_->NotifyChannelConnected();
 }
 
+MetroViewerProcessHost::InternalMessageFilter::~InternalMessageFilter() {
+}
+
 MetroViewerProcessHost::MetroViewerProcessHost(
     const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner) {
   DCHECK(!instance_);