backing out 4df2e13d4157 (bug 891993), to prevent build bustage from warnings in a 3rd-party .h file that'll be landing in Bug 837199.
Bug 897718 - Remove unused JSAPI method JS_CallGenericTracer; r=jonco

--HG--
extra : rebase_source : 42641b92f4228a6cbccc9c7c6d16333308748a80
Bug 897724 - Fix some opt build warnings in clang; r=sfink

--HG--
extra : rebase_source : af3aa90d6464fd6701e29d014782a9037a3b1afe
Bug 894288 - Prevent triggering an endless abort cycle when loading any tabs in the browser. r=BenWa