Bug 1024765 - Part 1: Add test-case for timers firing when the target thread is not running. r=bwc, a=1.3+

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extra : rebase_source : 936c598a51bfcb611c514f27ea26491228a79ea7
Bug 1024765 - Part 2: Make refcounting logic around PostTimerEvent more explicit. r=bz, a=1.3+

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extra : rebase_source : dba70197a132790b7ec0c1b1e6d61ad4a9d0cead