Bug 884897 - Convert SimplePush to WebIDL. r=khuey

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extra : amend_source : e2cdea6c33f920e90c9fb41ee3a3a5d4e80bd9a8
Bug 884897 - Remove dom_push.xpt from installers. r=dougt

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extra : amend_source : aa3296f0baed0891ad5bfa81472381c4db21b160