Implement ui::ClipboardMus.

ui/views/mus/window_manager_connection.h

Index: ui/views/mus/window_manager_connection.h
diff --git a/ui/views/mus/window_manager_connection.h b/ui/views/mus/window_manager_connection.h
index afcf368ab5653a8bafe7f8c9f834ede401a1f1fc..2325672c22f014c198550ec05fbaa7e84dd40016 100644
--- a/ui/views/mus/window_manager_connection.h
+++ b/ui/views/mus/window_manager_connection.h
@@ -22,6 +22,7 @@ class Connector;
 }
 
 namespace views {
+class ClipboardMus;
 class NativeWidget;
 class PointerWatcher;
 class ScreenMus;
@@ -31,6 +32,7 @@ class NativeWidgetDelegate;
 
 // Provides configuration to mus in views. This consists of the following:
 // . Provides a Screen implementation backed by mus.
+// . Provides a Clipboard implementation backed by mus.
 // . Creates and owns a WindowTreeClient.
 // . Registers itself as the factory for creating NativeWidgets so that a
 //   NativeWidgetMus is created.