[#174151612] fix bug: drag of attribute from plugin(including standalone Sage) causes Importer to be invoked.
[#174151612] fix bug: drag of attribute from plugin(including standalone Sage) causes Importer to be invoked.

concord-consortium/codap,concord-consortium/codap,concord-consortium/codap,concord-consortium/codap,concord-consortium/codap