Bug 929236 - Cache asm.js compiled code in Gecko (r=janv)

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extra : rebase_source : 1c97962da0044858c583fc45e69dd22e519b8066
Bug 929236 - Don't waste time caching small asm.js modules (r=sstangl)

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extra : rebase_source : 03c1f15c9ad89e0cae2e53a633ab743656380bf5