Bug 899696 - Fix unsafe reference hazard in SendToGenerator; r=sfink

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extra : rebase_source : 302da62f20ff1ddb14f35ddb8f3032b92961f6e0
Bug 899693 - Fix unsafe reference hazards around HashableValue::setValue; r=sfink

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extra : rebase_source : f296325db530ec1f94708a657cdc7ad885a85368