aura-mus: wire up drag and drop.

ui/views/mus/mus_client.h

Index: ui/views/mus/mus_client.h
diff --git a/ui/views/mus/mus_client.h b/ui/views/mus/mus_client.h
index 3e881c5d84d8dac4cf5b55e1b409ba1bcbfcb50b..829a04997f4cdd5a2805c80fa921c64c35820943 100644
--- a/ui/views/mus/mus_client.h
+++ b/ui/views/mus/mus_client.h
@@ -15,7 +15,6 @@
 #include "services/service_manager/public/cpp/identity.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/aura/mus/window_tree_client_delegate.h"
-#include "ui/base/dragdrop/os_exchange_data_provider_factory.h"
 #include "ui/views/mus/mus_export.h"
 #include "ui/views/mus/screen_mus_delegate.h"
 #include "ui/views/widget/widget.h"
@@ -61,10 +60,8 @@ class MusClientTestApi;
 // MusClient establishes a connection to mus and sets up necessary state so that
 // aura and views target mus. This class is useful for typical clients, not the
 // WindowManager. Most clients don't create this directly, rather use AuraInit.
-class VIEWS_MUS_EXPORT MusClient
-    : public aura::WindowTreeClientDelegate,
-      public ScreenMusDelegate,
-      public ui::OSExchangeDataProviderFactory::Factory {
+class VIEWS_MUS_EXPORT MusClient : public aura::WindowTreeClientDelegate,
+                                   public ScreenMusDelegate {
  public:
   // Most clients should use AuraInit, which creates a MusClient.
   // |create_wm_state| indicates whether MusClient should create a wm::WMState.
@@ -135,9 +132,6 @@ class VIEWS_MUS_EXPORT MusClient
   void OnWindowManagerFrameValuesChanged() override;
   aura::Window* GetWindowAtScreenPoint(const gfx::Point& point) override;
 
-  // ui:OSExchangeDataProviderFactory::Factory:
-  std::unique_ptr<OSExchangeData::Provider> BuildProvider() override;
-
   static MusClient* instance_;
 
   service_manager::Identity identity_;