Bug 1093307 - Part 0: Cancel background allocation before flushing empty chunks when we OOM; r=jonco

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extra : rebase_source : 6859fba8d90df935cc109d67268650b9c251c372
Bug 1074961 - Part 10: move foreground sweeping of background things closer to background sweeping; r=jonco

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extra : rebase_source : fed8085405ca3ed46ceb3f53a1aec63c2cd9a421
Bug 1093307 - Part 1: Shrinking GC's already sweep on the foreground so remove the flag; r=jonco

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extra : rebase_source : 521266ba686047388ddb1832d6a4f83f0bcf3410