See https://uberchromegw.corp.google.com/i/chromeos.chrome/builders/veyron_minnie-tot-chrome-pfq-informational/builds/3860 as an example. Actually it started show up on almost all the informational builders (see https://uberchromegw.corp.google.com/i/chromeos.chrome/waterfall?reload=300).  

Selected Error message:
arc-camera3-test-0.0.1-r42: /build/veyron_minnie/tmp/portage/media-libs/arc-camera3-test-0.0.1-r42/work/arc-camera3-test-0.0.1/android/include/hardware/libhardware/include/hardware/camera3.h:20:10: fatal error: 
arc-camera3-test-0.0.1-r42:       'system/camera_metadata.h' file not found
arc-camera3-test-0.0.1-r42: #include <system/camera_metadata.h>
arc-camera3-test-0.0.1-r42:          ^~~~~~~~~~~~~~~~~~~~~~~~~~
arc-camera3-test-0.0.1-r42: 1 error generated.
arc-camera3-test-0.0.1-r42: 1 error generated.
arc-camera3-test-0.0.1-r42: make[1]: *** [common.mk:933: camera3_test/camera3_module_test.pie.o] Error 1
arc-camera3-test-0.0.1-r42: make[1]: *** Waiting for unfinished jobs....
arc-camera3-test-0.0.1-r42: 1 error generated.
arc-camera3-test-0.0.1-r42: make[1]: Leaving directory '/build/veyron_minnie/tmp/portage/media-libs/arc-camera3-test-0.0.1-r42/work/arc-camera3-test-0.0.1'
arc-camera3-test-0.0.1-r42: make: *** [common.mk:171: camera3_test/arc_camera3_test] Error 2
arc-camera3-test-0.0.1-r42:  * ERROR: media-libs/arc-camera3-test-0.0.1-r42::chromiumos failed (compile phase):
arc-camera3-test-0.0.1-r42:  *   emake failed
Failed media-libs/arc-camera3-test-0.0.1-r42 (in 0m2.8s). Your build has failed.
Pending 4/674, [Time 11:19:55 | Elapsed 45m36.3s | Load 1.94 4.72 13.3]
Packages failed:
	media-libs/arc-camera3-test-0.0.1-r42
ERROR   : Fri Apr 21 11:19:56 PDT 2017
ERROR   :  PGID  PPID   PID     ELAPSED     TIME %CPU COMMAND
ERROR   : Arguments of 10: ./build_packages '--board=veyron_minnie' '--accept_licenses=@CHROMEOS' '--withdebugsymbols' '--skip_chroot_upgrade' '--noworkon' '--withevents' '--eventfile=/mnt/host/source/buildbot_archive/veyron_minnie-tot-chrome-pfq-informational/R60-9482.0.0-b3860/build-events.json' 'virtual/target-os' 'virtual/target-os-dev' 'virtual/target-os-test' 'virtual/target-os-factory' 'virtual/target-os-factory-shim' 'chromeos-base/autotest-all'
ERROR   : Backtrace:  (most recent call is last)
ERROR   :  build_packages:307:main(), called: die_err_trap  
ERROR   : 
ERROR   : Command failed:
ERROR   :   Command '( if [[ "${FLAGS_run_goma}" -eq "${FLAGS_TRUE}" ]]; then
ERROR   :     info "Starting goma compiler_proxy."; goma_ctl="${GOMA_DIR:-${HOME}/goma}/goma_ctl.py"; "${goma_ctl}" restart; trap "\"${goma_ctl}\" stop" EXIT;
ERROR   : fi; set -o pipefail; sudo -E "${EMERGE_CMD[@]}" "${EMERGE_FLAGS[@]}" "${PACKAGES[@]}" | tee "${tmpfile}" )' exited with nonzero code: 1
11:19:56: ERROR: 
return code: 1; command: /b/cbuild/repository/chromite/bin/cros_sdk '--chrome_root=/b/cbuild/repository/.cache/distfiles/target-master/chrome-src-internal' 'PARALLEL_EMERGE_STATUS_FILE=/tmp/tmpbb7FTK' 'USE=chrome_internal' 'FEATURES=separatedebug' 'CHROME_ORIGIN=LOCAL_SOURCE' -- ./build_packages '--board=veyron_minnie' '--accept_licenses=@CHROMEOS' --withdebugsymbols --skip_chroot_upgrade --noworkon --withevents '--eventfile=/mnt/host/source/buildbot_archive/veyron_minnie-tot-chrome-pfq-informational/R60-9482.0.0-b3860/build-events.json' virtual/target-os virtual/target-os-dev virtual/target-os-test virtual/target-os-factory virtual/target-os-factory-shim chromeos-base/autotest-all
cmd=['/b/cbuild/repository/chromite/bin/cros_sdk', '--chrome_root=/b/cbuild/repository/.cache/distfiles/target-master/chrome-src-internal', 'PARALLEL_EMERGE_STATUS_FILE=/tmp/tmpbb7FTK', u'USE=chrome_internal', 'FEATURES=separatedebug', 'CHROME_ORIGIN=LOCAL_SOURCE', '--', './build_packages', u'--board=veyron_minnie', '--accept_licenses=@CHROMEOS', '--withdebugsymbols', '--skip_chroot_upgrade', '--noworkon', '--withevents', u'--eventfile=/mnt/host/source/buildbot_archive/veyron_minnie-tot-chrome-pfq-informational/R60-9482.0.0-b3860/build-events.json', 'virtual/target-os', 'virtual/target-os-dev', 'virtual/target-os-test', 'virtual/target-os-factory', 'virtual/target-os-factory-shim', 'chromeos-base/autotest-all'], cwd=/b/cbuild/repository, extra env={'PARALLEL_EMERGE_STATUS_FILE': '/tmp/tmpbb7FTK', 'USE': u'chrome_internal', 'FEATURES': 'separatedebug', 'CHROME_ORIGIN': 'LOCAL_SOURCE'}

At first I thought it was caused by jcliang@'s arc-camera CLs as they broke CQ this morning and have the same symptom, which later all got reverted. But the failure stayed in the informational builders and didn't go away at all. 


akeshet@ suggested that a green CQ would likely fix this. Let's keep this bug open until it's confirmed fixed by CQ. At the current moment I'll assign to the owner of the arc-camera CLs.