fix: drag and drop should copy on macOS (#35978)

fix: drag and drop should copy on macOS (#35963)

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

shell/browser/ui/drag_util_mac.mm

@@ -20,7 +20,8 @@ @implementation DragDownloadItemSource
 
 - (NSDragOperation)draggingSession:(NSDraggingSession*)session
     sourceOperationMaskForDraggingContext:(NSDraggingContext)context {
-  return NSDragOperationEvery;
+  return context == NSDraggingContextOutsideApplication ? NSDragOperationCopy
+                                                        : NSDragOperationEvery;
 }
 
 @end
@@ -70,7 +71,7 @@ void DragFileItems(const std::vector<base::FilePath>& files,
   NSEvent* dragEvent =
       [NSEvent mouseEventWithType:NSEventTypeLeftMouseDragged
                          location:position
-                    modifierFlags:NSEventMaskLeftMouseDragged
+                    modifierFlags:0
                         timestamp:eventTime
                      windowNumber:[[native_view window] windowNumber]
                           context:nil