Bug 1074561 - Allow media plugins to run on Linuxes without sandboxing support. r=jesup

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extra : amend_source : dcbbf2bcbb8481e60504c1483a61627bde4850a2
Bug 1074561 - Disable EME plugins on Linux if sandboxing is unavailable. r=jesup

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extra : amend_source : 5e2192974cce18fd94abff72c9def32cfbaf675d