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

ui/aura/mus/window_tree_client.cc

 // Copyright 2014 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_tree_client.h"
 
 #include <stddef.h>
 
 #include <string>
 #include <utility>
@@ skipping 1665 matching lines @@
   base::Optional<gfx::Rect> out_rect = base::nullopt;
   if (mask_rect) {
     out_rect = gfx::ConvertRectToPixel(ScaleFactorForDisplay(window),
                                        mask_rect.value());
   }
 
   tree_->SetHitTestMask(WindowMus::Get(window_tree_host->window())->server_id(),
                         out_rect);
 }
 
+void WindowTreeClient::OnWindowTreeHostSetOpacity(
+    WindowTreeHostMus* window_tree_host,
+    float opacity) {
+  WindowMus* window = WindowMus::Get(window_tree_host->window());
+  const uint32_t change_id = ScheduleInFlightChange(
+      base::MakeUnique<CrashInFlightChange>(window, ChangeType::OPACITY));
+  tree_->SetWindowOpacity(change_id, window->server_id(), opacity);
+}
+
 void WindowTreeClient::OnWindowTreeHostDeactivateWindow(
     WindowTreeHostMus* window_tree_host) {
   tree_->DeactivateWindow(
       WindowMus::Get(window_tree_host->window())->server_id());
 }
 
 void WindowTreeClient::OnWindowTreeHostStackAbove(
     WindowTreeHostMus* window_tree_host,
     Window* window) {
   WindowMus* above = WindowMus::Get(window_tree_host->window());
@@ skipping 140 matching lines @@
   return ScheduleInFlightChange(base::MakeUnique<InFlightCaptureChange>(
       this, capture_synchronizer_.get(), window));
 }
 
 uint32_t WindowTreeClient::CreateChangeIdForFocus(WindowMus* window) {
   return ScheduleInFlightChange(base::MakeUnique<InFlightFocusChange>(
       this, focus_synchronizer_.get(), window));
 }
 
 }  // namespace aura