The key event should be stopped propagation when it's been processed as an accelerator.

ui/views/mus/native_widget_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/native_widget_mus.h"
 
 #include "base/macros.h"
 #include "base/thread_task_runner_handle.h"
 #include "components/mus/public/cpp/property_type_converters.h"
 #include "components/mus/public/cpp/window.h"
@@ skipping 803 matching lines @@
     // If such object is not attached, character events might be sent (e.g. on
     // Windows). In this case, we just skip these.
     return;
   }
   // Renderer may send a key event back to us if the key event wasn't handled,
   // and the window may be invisible by that time.
   if (!content_->IsVisible())
     return;
 
   native_widget_delegate_->OnKeyEvent(event);
-  if (event->handled())
-    return;
-
-  if (GetWidget()->HasFocusManager() &&
-      !GetWidget()->GetFocusManager()->OnKeyEvent(*event))
-    event->SetHandled();
 }
 
 void NativeWidgetMus::OnMouseEvent(ui::MouseEvent* event) {
   // TODO(sky): forward to tooltipmanager. See NativeWidgetDesktopAura.
   DCHECK(content_->IsVisible());
   native_widget_delegate_->OnMouseEvent(event);
   // WARNING: we may have been deleted.
 }
 
 void NativeWidgetMus::OnScrollEvent(ui::ScrollEvent* event) {
@@ skipping 14 matching lines @@
 
 void NativeWidgetMus::OnGestureEvent(ui::GestureEvent* event) {
   native_widget_delegate_->OnGestureEvent(event);
 }
 
 void NativeWidgetMus::OnHostCloseRequested(const aura::WindowTreeHost* host) {
   GetWidget()->Close();
 }
 
 }  // namespace views