Bug 849273 - Investigate splitting the js and JS namespaces r=terrence

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extra : rebase_source : 2b131d0177f02e5f0e89398545481fcacbfde00f
Bug 848754 - GC: Remove relaxed root checking infrastructure r=terrence

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extra : rebase_source : 7f781b1c7edbae14ce9b2fd4d45c44e8cb5c2968