mus: Implement interwindow drag and drop

services/ui/ws/event_dispatcher.cc

Index: services/ui/ws/event_dispatcher.cc
diff --git a/services/ui/ws/event_dispatcher.cc b/services/ui/ws/event_dispatcher.cc
index 06c632338126f2ff3003a0152083913836d6ee5e..2494d427a110e9e9302aa247528bb3aca68a88c5 100644
--- a/services/ui/ws/event_dispatcher.cc
+++ b/services/ui/ws/event_dispatcher.cc
@@ -8,6 +8,8 @@
 
 #include "base/time/time.h"
 #include "services/ui/ws/accelerator.h"
+#include "services/ui/ws/current_drag_operation.h"
+#include "services/ui/ws/current_drag_operation_delegate.h"
 #include "services/ui/ws/display.h"
 #include "services/ui/ws/event_dispatcher_delegate.h"
 #include "services/ui/ws/server_window.h"
@@ -188,6 +190,17 @@ bool EventDispatcher::SetCaptureWindow(ServerWindow* window,
   return true;
 }
 
+void EventDispatcher::SetDragDropSourceWindow(
+    uint32_t change_id,
+    WindowTree* window_tree,
+    ServerWindow* capture_window,
+    mojo::Map<mojo::String, mojo::Array<uint8_t>> mime_data,
+    uint32_t drag_operations) {
+  current_drag_drop_operation_.reset(
+      new CurrentDragOperation(this, change_id, window_tree, capture_window,
+                               std::move(mime_data), drag_operations));
+}
+
 void EventDispatcher::AddSystemModalWindow(ServerWindow* window) {
   modal_window_controller_.AddSystemModalWindow(window);
 }
@@ -341,6 +354,15 @@ void EventDispatcher::ProcessLocatedEvent(const ui::LocatedEvent& event) {
       mouse_button_down_ = false;
   }
 
+  if (current_drag_drop_operation_) {
+    const PointerTarget target = PointerTargetForEvent(event);
+    const ClientSpecificId client_id = delegate_->GetEventTargetClientId(
+        target.window, target.in_nonclient_area);
+    current_drag_drop_operation_->DispatchLocatedEvent(event, target.window,
+                                                       client_id);
+    return;
+  }
+
   if (capture_window_) {
     mouse_cursor_source_window_ = capture_window_;
     DispatchToClient(capture_window_, capture_window_client_id_, event);
@@ -575,5 +597,9 @@ void EventDispatcher::OnWindowDestroyed(ServerWindow* window) {
     mouse_cursor_source_window_ = nullptr;
 }
 
+void EventDispatcher::OnDragOver(bool success) {
+  current_drag_drop_operation_.reset();
+}
+
 }  // namespace ws
 }  // namespace ui