YARN-947. Implementing the data objects to be used by the History reader and writer interfaces. Contributed by Zhijie Shen.
svn merge --ignore-ancestry -c 1556692 ../YARN-321


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1562159 13f79535-47bb-0310-9956-ffa450edef68