Implement and test aura::client::CaptureClient in views::NativeWidgetMus for plumbing (Set|Release)…

ui/views/mus/native_widget_mus.h

Index: ui/views/mus/native_widget_mus.h
diff --git a/ui/views/mus/native_widget_mus.h b/ui/views/mus/native_widget_mus.h
index 7532719db35e7a0532bd40dc2181af36c412d071..fbbb3d812f303fa6f78d59e14c0c2f395dfae733 100644
--- a/ui/views/mus/native_widget_mus.h
+++ b/ui/views/mus/native_widget_mus.h
@@ -227,6 +227,7 @@ class VIEWS_MUS_EXPORT NativeWidgetMus
 private:
   friend class NativeWidgetMusTest;
   class MusWindowObserver;
+  class MusCaptureClient;
 
   ui::PlatformWindowDelegate* platform_window_delegate() {
     return window_tree_host();
@@ -258,7 +259,7 @@ private:
   std::unique_ptr<WindowTreeHostMus> window_tree_host_;
   aura::Window* content_;
   std::unique_ptr<wm::FocusController> focus_client_;
-  std::unique_ptr<aura::client::DefaultCaptureClient> capture_client_;
+  std::unique_ptr<MusCaptureClient> capture_client_;
   std::unique_ptr<aura::client::WindowTreeClient> window_tree_client_;
   std::unique_ptr<aura::client::ScreenPositionClient> screen_position_client_;
   std::unique_ptr<wm::CursorManager> cursor_manager_;