:DragSource*Ended* functions after returning false (0).
Return true (1) to handle the drag operation. Call
:DragSourceEndedAt and DragSourceSystemDragEnded either synchronously or asynchronously to inform the web view that the drag operation has ended.
Called when the user starts dragging content in the web view. Contextual information about the dragged content is supplied by |drag_data|. (|x|, |y|) is the drag start location in screen coordinates. OS APIs that run a system message loop may be used within the StartDragging call.
Return false (0) to abort the drag operation. Don't call any of