Go here:
https://ci.chromium.org/p/chromium/g/chromium.android/console?limit=200
Note that Cronet lollipop builder frequently fails.
See attached screenshot for example.

I looked into 4 failures.
All were crashes.
3 were in CronetTestRuleTest.
1 didn't have the crashing test mentioned in the logcat.
3 were some kind of GC crash:
F libc    : Fatal signal 11 (SIGSEGV), code 1, fault addr 0x30c in tid 13408 (roidJUnitRunner)
I DEBUG   : *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
I DEBUG   : Build fingerprint: 'google/hammerhead/hammerhead:5.1.1/LMY48I/2074855:userdebug/dev-keys'
I DEBUG   : Revision: '11'
I DEBUG   : ABI: 'arm'
I DEBUG   : pid: 13389, tid: 13408, name: roidJUnitRunner  >>> org.chromium.net <<<
I DEBUG   : signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x30c
I DEBUG   :     r0 0000bf71  r1 b47fcfc8  r2 7170fdf8  r3 b4838830
I DEBUG   :     r4 00000003  r5 12e05000  r6 b4896c40  r7 0000bf75
I DEBUG   :     r8 00000300  r9 b47faa70  sl af2b0ea8  fp 00000001
I DEBUG   :     ip af2b0eac  sp af2b0e68  lr b4560757  pc b4624d02  cpsr 20070030
I DEBUG   : 
I DEBUG   : backtrace:
I DEBUG   :     #00 pc 0012fd02  /system/lib/libart.so (art::gc::collector::MarkSweep::ProcessMarkStack(bool)+197)
I DEBUG   :     #01 pc 001304f9  /system/lib/libart.so (art::gc::collector::MarkSweep::MarkReachableObjects()+40)
I DEBUG   :     #02 pc 0013038f  /system/lib/libart.so (art::gc::collector::MarkSweep::MarkingPhase()+122)
I DEBUG   :     #03 pc 00130479  /system/lib/libart.so (art::gc::collector::MarkSweep::RunPhases()+176)
I DEBUG   :     #04 pc 00127067  /system/lib/libart.so (art::gc::collector::GarbageCollector::Run(art::gc::GcCause, bool)+246)
I DEBUG   :     #05 pc 001460af  /system/lib/libart.so (art::gc::Heap::CollectGarbageInternal(art::gc::collector::GcType, art::gc::GcCause, bool)+1406)
I DEBUG   :     #06 pc 002078af  /system/lib/libart.so (art::Runtime_gc(_JNIEnv*, _jclass*)+30)
I DEBUG   :     #07 pc 000003df  /data/dalvik-cache/arm/system@framework@boot.oat

I have suspicions that this is an Android ART GC bug that was fixed before Marshmallow.
 

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