mus: Implement interwindow drag and drop

services/ui/ws/event_dispatcher.h

Index: services/ui/ws/event_dispatcher.h
diff --git a/services/ui/ws/event_dispatcher.h b/services/ui/ws/event_dispatcher.h
index 0bbac9e0417285c36b32f4ec09421fbc6ee6c1f6..231e59d94bf8389bfefd6088a32d8cb616b63238 100644
--- a/services/ui/ws/event_dispatcher.h
+++ b/services/ui/ws/event_dispatcher.h
@@ -14,6 +14,7 @@
 #include "base/macros.h"
 #include "services/ui/common/types.h"
 #include "services/ui/public/interfaces/event_matcher.mojom.h"
+#include "services/ui/ws/current_drag_operation_source.h"
 #include "services/ui/ws/modal_window_controller.h"
 #include "services/ui/ws/server_window_observer.h"
 #include "ui/gfx/geometry/rect_f.h"
@@ -26,8 +27,10 @@ class LocatedEvent;
 namespace ws {
 
 class Accelerator;
+class CurrentDragOperation;
 class EventDispatcherDelegate;
 class ServerWindow;
+class WindowTree;
 
 namespace test {
 class EventDispatcherTestApi;
@@ -75,6 +78,13 @@ class EventDispatcher : public ServerWindowObserver {
     return capture_window_client_id_;
   }
 
+  void SetDragDropSourceWindow(
+      CurrentDragOperationSource* drag_source,
+      ServerWindow* window,
+      mojo::Map<mojo::String, mojo::Array<uint8_t>> mime_data,
+      uint32_t drag_operations);
+  void EndDragDrop();
+
   // Adds a system modal window. The window remains modal to system until it is
   // destroyed. There can exist multiple system modal windows, in which case the
   // one that is visible and added most recently or shown most recently would be
@@ -216,6 +226,8 @@ class EventDispatcher : public ServerWindowObserver {
   ServerWindow* capture_window_;
   ClientSpecificId capture_window_client_id_;
 
+  std::unique_ptr<CurrentDragOperation> current_drag_drop_operation_;
+
   ModalWindowController modal_window_controller_;
 
   bool mouse_button_down_;