Bug 1072801 - Handle OOM when allocating GC statistics slice with an immediate crash; r=sfink

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extra : rebase_source : de1dc271c953b92349053324443358d4b5c98be8
Bug 1074942 - Split out background allocation into a separate task; r=bhackett

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extra : rebase_source : bbf7db71c685d2fb8b271da7fb21b97b3466044f