Keep non-key event handling in-house for NativeWidgetMus

ui/views/mus/window_tree_host_mus.cc

Index: ui/views/mus/window_tree_host_mus.cc
diff --git a/ui/views/mus/window_tree_host_mus.cc b/ui/views/mus/window_tree_host_mus.cc
index 3251c96febfb4349bfa649da5436a64fdf3e9f7b..25194f54980ad63cc6b3a3888818ad91ab714624 100644
--- a/ui/views/mus/window_tree_host_mus.cc
+++ b/ui/views/mus/window_tree_host_mus.cc
@@ -72,7 +72,10 @@ WindowTreeHostMus::~WindowTreeHostMus() {
 }
 
 void WindowTreeHostMus::DispatchEvent(ui::Event* event) {
-  if (event->IsKeyEvent() && GetInputMethod()) {
+  // TODO(markdittmer): This flow is going away. For now, it is only intended
+  // for managing key events.
+  DCHECK(event->IsKeyEvent());
+  if (GetInputMethod()) {
     GetInputMethod()->DispatchKeyEvent(event->AsKeyEvent());
     event->StopPropagation();
     return;