Bug 944821 - Support more than 1 cached asm.js module per origin (r=janv)

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rename : js/xpconnect/tests/mochitest/file_asmjs.js => dom/asmjscache/test/file_slow.js
rename : js/xpconnect/tests/mochitest/test_asmjs2.html => dom/asmjscache/test/test_cachingBasic.html
rename : js/xpconnect/tests/mochitest/test_asmjs.html => dom/asmjscache/test/test_slow.html
rename : js/xpconnect/tests/mochitest/test_asmjs3.html => dom/asmjscache/test/test_workers.html
extra : rebase_source : 14efc458193762f5be99dfff78d353a63f3fc45a