Bug 1007520 - Part 2: Avoid leaking Activities.callers in ActivitiesService.jsm. r=fabrice a=khuey

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extra : rebase_source : 97750b3623e78926191533450bcbf1139bd35d1c
Bug 1007520 - Part 3: Avoid leaking SpecialPowers to nsInProcessTabChildGlobal.mMessageManager. r=ted a=khuey

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extra : rebase_source : 74b98cc5bd0024f1178d3b929aefa9534370b79d