Bug 984048 - Patch 4 - Handle parse and uncaught errors. r=khuey

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extra : rebase_source : 463146233c874c2f2c63c018f2a43a66ca9ea49a
Bug 984048 - Patch 5 - ServiceWorker [[Install]] algorithm. r=ehsan, khuey

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extra : rebase_source : 6c710937fde2ebe679908690c1295927eb4c195d