code: function saveNameToExportMap(index, def, exportsMap) {
      if (exportsMap) {
          if (def.exportAs)
              exportsMap[def.exportAs] = index;
          if (def.template)
              exportsMap[''] = index;
      }
  }
docs: Builds up an export map as directives are created, so local refs can be quickly mapped
  to their directive instances.