This patch:
1. Introduces PerformanceServerTiming.webidl.
2. Adds serverTiming in PerformanceResourceTiming.webidl.
3. Gets serverTiming data from nsITimedChannel and keeps it in the PerformanceTimng class.
MozReview-Commit-ID: 9mkGkHbxopC
--HG--
extra : rebase_source : 7e0d0321e71eb0af9591ead76dc163996fbaf819