It seems since we moved over to Swarming for test execution, we lost the leak detection for our ASan bots. machenbach@ tipped me this might be the case since V8 hit a similar problem and with https://codereview.webrtc.org/2868443002/#ps1 I verified it's the case.

After looking at a build I can see that 
ASAN_OPTIONS=symbolize=0
i.e. it's missing the detect_leaks=1 line. 
One way to get that is to use this place where it's added: https://cs.chromium.org/chromium/src/testing/test_env.py?rcl=4d49107dce95a5491acebfab01023a377ae03b58&l=89
We used to pass --lsan=1 to our tests via the recipes when we ran these tests pre-Swarming, but we now use mb.py for generating these command lines.

It seems to be easy to fix though, by just adding a line for LSan here:
https://chromium.googlesource.com/external/webrtc/+/master/tools-webrtc/mb/mb.py#1127
but the Chromium mb.py doesn't have that, so the Chromium bots somehow enable it in another way.

See https://codereview.webrtc.org/2868443002/