Bug 1347823 - Part 2: Move HistoryTracker to nsSHistory and bind its event target to the TabGroup. r=smaug

Convert the singleton HistoryTracker implementation to a per-nsSHistory based
implementation so that it can be bound to a TabGroup.

MozReview-Commit-ID: 7cMtArsO5lQ

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extra : rebase_source : 3711bc7f7afaa40772035e24270d4fde1d17924a