Keep non-key event handling in-house for NativeWidgetMus

ui/views/mus/window_tree_host_mus.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/mus/window_tree_host_mus.h"
 
 #include "base/memory/ptr_util.h"
 #include "components/bitmap_uploader/bitmap_uploader.h"
 #include "components/mus/public/cpp/window.h"
 #include "ui/aura/window.h"
@@ skipping 55 matching lines @@
   input_method_.reset(new InputMethodMUS(this, window));
   SetSharedInputMethod(input_method_.get());
 }
 
 WindowTreeHostMus::~WindowTreeHostMus() {
   DestroyCompositor();
   DestroyDispatcher();
 }
 
 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;
   }
   WindowTreeHostPlatform::DispatchEvent(event);
 }
 
 void WindowTreeHostMus::OnClosed() {
   if (native_widget_)
     native_widget_->OnPlatformWindowClosed();
 }
 
 void WindowTreeHostMus::OnActivationChanged(bool active) {
   if (active)
     GetInputMethod()->OnFocus();
   else
     GetInputMethod()->OnBlur();
   if (native_widget_)
     native_widget_->OnActivationChanged(active);
   WindowTreeHostPlatform::OnActivationChanged(active);
 }
 
 void WindowTreeHostMus::OnCloseRequest() {
   OnHostCloseRequested();
 }
 
 }  // namespace views