aura-mus: Implement DesktopWindowTreeHostMus::SetOpacity().

ui/aura/mus/window_port_mus.cc

 // Copyright 2016 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/aura/mus/window_port_mus.h"
 
 #include "base/memory/ptr_util.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/transient_window_client.h"
 #include "ui/aura/mus/client_surface_embedder.h"
@@ skipping 206 matching lines @@
   ServerChangeData data;
   data.visible = visible;
   ScopedServerChange change(this, ServerChangeType::VISIBLE, data);
   if (visible)
     window_->Show();
   else
     window_->Hide();
 }
 
 void WindowPortMus::SetOpacityFromServer(float opacity) {
-  // TODO(sky): route to server.
-  // Changes to opacity don't make it back to the server.
   window_->layer()->SetOpacity(opacity);
 }
 
 void WindowPortMus::SetPredefinedCursorFromServer(ui::mojom::Cursor cursor) {
   // As this does nothing more than set the cursor we don't need to use
   // ServerChange.
   predefined_cursor_ = cursor;
 }
 
 void WindowPortMus::SetPropertyFromServer(
@@ skipping 204 matching lines @@
   change_data.property_name =
       GetPropertyConverter()->GetTransportNameForPropertyKey(key);
   // TODO(sky): investigate to see if we need to compare data. In particular do
   // we ever have a case where changing a property cascades into changing the
   // same property?
   if (!RemoveChangeByTypeAndData(ServerChangeType::PROPERTY, change_data))
     window_tree_client_->OnWindowMusPropertyChanged(this, key, std::move(data));
 }
 
 }  // namespace aura