Bug 937960, part 1 - Add ICC pref to nsJSEnv. r=smaug
Bug 937960, part 2 - Add ICC slice timer and scheduling. r=smaug
Bug 937960, part 3 - Pass in a small time budget with ICC. r=smaug
Bug 937960, part 4 - Reduce time until CC when it is incremental. r=smaug
Bug 948554, part 1 - Rename PrepareForCycleCollection and make it a method. r=smaug

This name is more precise, because we must call it once per slice,
not once per CC.  Being a method on the CC stats object is more consistent.
Bug 948554, part 2 - Convert some of nsJSEnvironment to TimeStamp for greater precision. r=smaug
Bug 948554, part 3 - Capture max slice time in logs and telemetry. r=smaug