[task 2021-06-08T15:04:08.793Z] 15:04:08     INFO -  24:24.96 TEST-UNEXPECTED-FAIL | valgrind-test | 24 bytes in 1 blocks are definitely lost at malloc / wr_thread_pool_new / WebRenderThreadPool / RenderThread
[task 2021-06-08T15:04:08.793Z] 15:04:08     INFO -  24:24.96 ==16107== 24 bytes in 1 blocks are definitely lost in loss record 3,311 of 10,861
[task 2021-06-08T15:04:08.794Z] 15:04:08     INFO -  24:24.96 ==16107==    at 0x4C28FC0: malloc+112 (vg_replace_malloc.c:307)
[task 2021-06-08T15:04:08.794Z] 15:04:08     INFO -  24:24.96 ==16107==    by 0x162F6CC9: wr_thread_pool_new+2729 (library/std/src/sys/unix/alloc.rs:14)
[task 2021-06-08T15:04:08.794Z] 15:04:08     INFO -  24:24.96 ==16107==    by 0x11EB0814: WebRenderThreadPool (checkouts/gecko/gfx/webrender_bindings/RenderThread.cpp:1037)
[task 2021-06-08T15:04:08.794Z] 15:04:08     INFO -  24:24.96 ==16107==    by 0x11EB0814: RenderThread (checkouts/gecko/gfx/webrender_bindings/RenderThread.cpp:64)
[task 2021-06-08T15:04:08.794Z] 15:04:08     INFO -  24:24.96 ==16107==    by 0x11EB0814: mozilla::wr::RenderThread::Start()+116 (checkouts/gecko/gfx/webrender_bindings/RenderThread.cpp:96)
[task 2021-06-08T15:04:08.795Z] 15:04:08     INFO -  24:24.96 ==16107==    by 0x11DE0FCD: gfxPlatform::InitLayersIPC()+93 (checkouts/gecko/gfx/thebes/gfxPlatform.cpp:1325)
[task 2021-06-08T15:04:08.795Z] 15:04:08     INFO -  24:24.96 ==16107==    by 0x11DDFBCF: gfxPlatform::Init()+2959 (checkouts/gecko/gfx/thebes/gfxPlatform.cpp:965)
[task 2021-06-08T15:04:08.795Z] 15:04:08     INFO -  24:24.96 ==16107==    by 0x11DDF00F: gfxPlatform::GetPlatform()+31 (checkouts/gecko/gfx/thebes/gfxPlatform.cpp:481)

https://treeherder.mozilla.org/jobs?repo=try&revision=3e44185e463f55bd96db2b8538d01e01df0a1462&selectedTaskRun=WvrRCWuXTPyTHsu1ZB4xoQ.0

This is very likely: https://searchfox.org/mozilla-central/rev/e8904db16ac45bff0ffe65e7289f8d2f00c48c48/gfx/webrender_bindings/src/bindings.rs#1098

FWIW we do shut down the style thread pool on shutdown like this: https://searchfox.org/mozilla-central/rev/e8904db16ac45bff0ffe65e7289f8d2f00c48c48/xpcom/build/XPCOMInit.cpp#790

Not super-duper amazing though.

This was fixed in bug 1715132.