code: function handleEditorChange(session, document, previousDocument) {
              if (addFilesPromise === null) {
                  doEditorChange(session, document, previousDocument);
              } else {
                  addFilesPromise.done(function () {
                      doEditorChange(session, document, previousDocument);
                  });
              }
          }
docs: Called each time a new editor becomes active.
  
  @param {Session} session - the active hinting session (TODO: currently unused by doEditorChange())
  @param {!Document} document - the document of the editor that has changed
  @param {?Document} previousDocument - the document of the editor is changing from