Bug 859335 - Make sure that the chunk passed to WriteZeroesToAudioBlock is not null; r=roc

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extra : rebase_source : 8a2b5bd19cdb12289950ff58ca72b85e99ba44a7
Bug 857600 - Add a mach command for debugging using gdb; r=gps

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extra : rebase_source : 85d0d7e717eb8ee92a61bd0ce7fd310ac2d3d715