Implements PerformanceTiming, nsITimedChannel, and devtools 'tls setup'
Also captures telemetry on this as we do for all other attributes of timedChannel
Also propogates some null transaction timings onto first real
transaction of a connection
MozReview-Commit-ID: 47TQJYVHnKC
This patch adds a jsonifier declaration to WebIDL's. The declaration adds an autogenerated method toJSON() on the given webidl. This patch also adds jsonifier and toJSON() to PerformanceTiming.webidl, and performance.timing, respectively.
The valid annotations are [Throws], [GetterThrows], and [SetterThrows], which can all either take no value or
be set to MainThread or Workers if the throwing behavior is only happening on main thread or in workers
