Issue 822047  has been merged into this issue.

The last two builds failed browser_tests:

https://ci.chromium.org/buildbot/chromium.memory/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/

https://ci.chromium.org/buildbot/chromium.memory/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/26593
https://ci.chromium.org/buildbot/chromium.memory/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/26594

In build 26593, I see the following in the stdout of "MediaRouterIntegrationOneUABrowserTest.Basic":

https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.memory%2FLinux_Chromium_OS_ASan_LSan_Tests__1_%2F26593%2F%2B%2Frecipes%2Fsteps%2Fbrowser_tests%2F0%2Flogs%2FMediaRouterIntegrationOneUABrowserTest.Basic%2F0


[12237:12237:0315/050057.368266:FATAL:projecting_observer_chromeos.cc(51)] Check failed: casting_session_count_ > 0 (0 vs. 0)

Source code:
https://cs.chromium.org/chromium/src/ash/display/projecting_observer_chromeos.cc?rcl=d94f7320abebb53842d2151e9b8fd893390abfb2&l=51

Full stack:
[12237:12237:0315/050057.368266:FATAL:projecting_observer_chromeos.cc(51)] Check failed: casting_session_count_ > 0 (0 vs. 0)
#0 0x000000943691 (/b/s/w/ir/out/Release/browser_tests+0x943690)
#1 0x00000e8e962c (/b/s/w/ir/out/Release/browser_tests+0xe8e962b)
#2 0x00000e946143 (/b/s/w/ir/out/Release/browser_tests+0xe946142)
#3 0x000018ad36d4 (/b/s/w/ir/out/Release/browser_tests+0x18ad36d3)
#4 0x00001883b757 (/b/s/w/ir/out/Release/browser_tests+0x1883b756)
#5 0x00000ef723f7 (/b/s/w/ir/out/Release/browser_tests+0xef723f6)
#6 0x00000ef7547f (/b/s/w/ir/out/Release/browser_tests+0xef7547e)
#7 0x00000e8eaf74 (/b/s/w/ir/out/Release/browser_tests+0xe8eaf73)
#8 0x00000eb76101 (/b/s/w/ir/out/Release/browser_tests+0xeb76100)
#9 0x00000e968a2c (/b/s/w/ir/out/Release/browser_tests+0xe968a2b)
#10 0x00000e969591 (/b/s/w/ir/out/Release/browser_tests+0xe969590)
#11 0x00000e969ea6 (/b/s/w/ir/out/Release/browser_tests+0xe969ea5)
#12 0x00000e971d11 (/b/s/w/ir/out/Release/browser_tests+0xe971d10)
#13 0x00000e9673dc (/b/s/w/ir/out/Release/browser_tests+0xe9673db)
#14 0x00000ea0904e (/b/s/w/ir/out/Release/browser_tests+0xea0904d)
#15 0x0000101710a3 (/b/s/w/ir/out/Release/browser_tests+0x101710a2)
#16 0x00000ece325d (/b/s/w/ir/out/Release/browser_tests+0xece325c)
#17 0x00001006cdf6 (/b/s/w/ir/out/Release/browser_tests+0x1006cdf5)
#18 0x00000ede90a6 (/b/s/w/ir/out/Release/browser_tests+0xede90a5)
#19 0x00000ede616f (/b/s/w/ir/out/Release/browser_tests+0xede616e)
#20 0x000004eab1ca (/b/s/w/ir/out/Release/browser_tests+0x4eab1c9)
#21 0x000008c4ba28 (/b/s/w/ir/out/Release/browser_tests+0x8c4ba27)
#22 0x000009cee588 (/b/s/w/ir/out/Release/browser_tests+0x9cee587)
#23 0x000008c4769c (/b/s/w/ir/out/Release/browser_tests+0x8c4769b)
#24 0x000008c54f95 (/b/s/w/ir/out/Release/browser_tests+0x8c54f94)
#25 0x000008c400a0 (/b/s/w/ir/out/Release/browser_tests+0x8c4009f)
#26 0x00000e5f4e0c (/b/s/w/ir/out/Release/browser_tests+0xe5f4e0b)
#27 0x00000e5f82a9 (/b/s/w/ir/out/Release/browser_tests+0xe5f82a8)
#28 0x000015b539b7 (/b/s/w/ir/out/Release/browser_tests+0x15b539b6)
#29 0x00000e5f33bc (/b/s/w/ir/out/Release/browser_tests+0xe5f33bb)
#30 0x00001006b63d (/b/s/w/ir/out/Release/browser_tests+0x1006b63c)
#31 0x00000ecddf47 (/b/s/w/ir/out/Release/browser_tests+0xecddf46)
#32 0x000005b8318d (/b/s/w/ir/out/Release/browser_tests+0x5b8318c)
#33 0x000005b853b5 (/b/s/w/ir/out/Release/browser_tests+0x5b853b4)
#34 0x000005b86717 (/b/s/w/ir/out/Release/browser_tests+0x5b86716)
#35 0x000005baaeb7 (/b/s/w/ir/out/Release/browser_tests+0x5baaeb6)
#36 0x000005baa127 (/b/s/w/ir/out/Release/browser_tests+0x5baa126)
#37 0x00000ed28b0c (/b/s/w/ir/out/Release/browser_tests+0xed28b0b)
#38 0x00000e8ba463 (/b/s/w/ir/out/Release/browser_tests+0xe8ba462)
#39 0x0000101639f1 (/b/s/w/ir/out/Release/browser_tests+0x101639f0)
#40 0x00000e8bb27a (/b/s/w/ir/out/Release/browser_tests+0xe8bb279)
#41 0x00000e8ba27f (/b/s/w/ir/out/Release/browser_tests+0xe8ba27e)
#42 0x7f2602cadf45 (/lib/x86_64-linux-gnu/libc-2.19.so+0x21f44)
#43 0x0000008f7bda (/b/s/w/ir/out/Release/browser_tests+0x8f7bd9)

This line of code has not changed in a long time:

https://chromium.googlesource.com/chromium/src/+/72bce5264bdb62d32d684f1e9c639bb2932e695c/ash/display/projecting_observer_chromeos.cc

The crash can be seen easily at the end of this log:
https://chromium-swarm.appspot.com/task?id=3c4233f3844a3710&refresh=10&show_raw=1

Same error in build 26594:
https://chromium-swarm.appspot.com/task?id=3c427fca03f04410&refresh=10&show_raw=1

Ahmed: can you please take a look?  Thanks.

The failing test is MediaRouterIntegrationOneUABrowserTest.Basic. It is crashing at this DCHECK: https://cs.chromium.org/chromium/src/ash/display/projecting_observer_chromeos.cc?type=cs&q=ProjectingObserver::OnCastingSessionStartedOrStopped&sq=package:chromium&l=51

I'm not familiar with this test so forwarding to mfoltz@ for triage, cc'ing dnicoara@.