Bug 941821 - Fix an exact rooting hazard false positive across ForkJoin invocation; r=sfink

    // WARNING: This code runs ON THE PARALLEL WORKER THREAD.

    // Therefore, it should NOT access `cx_` in any way!

    // ForkJoinSlice already contains an AutoAssertNoGC; however, the analysis

    // does not propagate this type information. We duplicate the assertion

    // here for maximum clarity.

    JS::AutoAssertNoGC nogc(runtime());

    Allocator *allocator = allocators_[threadId];

    ForkJoinSlice slice(perThread, threadId, numSlices_, allocator,

                        this, &records_[threadId]);