docs: function addDependentKeys(desc, obj, keyName, meta) {
      // the descriptor has a list of dependent keys, so
      // add all of its dependent keys.
      var idx, len, depKey;
      var depKeys = desc._dependentKeys;
      if (!depKeys) {
        return;
      }
  
      for (idx = 0, len = depKeys.length; idx < len; idx++) {
        depKey = depKeys[idx];
        // Increment the number of times depKey depends on keyName.
        meta.writeDeps(depKey, keyName, (meta.peekDeps(depKey, keyName) || 0) + 1);
        // Watch the depKey
        _emberMetalWatching.watch(obj, depKey, meta);
      }
    }