Reilly, could you help triage?

I'm going to mark Flaky in a moment

Alexander, can you take a look at these first since they were recently added by your patch: https://chromium-review.googlesource.com/c/chromium/src/+/1087049

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c0dbb3daf5f5639ddd98f8601c9578d1b85d2d23

commit c0dbb3daf5f5639ddd98f8601c9578d1b85d2d23
Author: David Grogan <dgrogan@chromium.org>
Date: Thu Jun 21 21:51:36 2018

Sheriff: Mark a few sensor tests as flaky on Mac

TBR=alexander.shalamov@intel.com

Bug:  855222 
Change-Id: I5174582d08f61e9133849a2c21d0df3610e54400
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/1110955
Reviewed-by: David Grogan <dgrogan@chromium.org>
Commit-Queue: David Grogan <dgrogan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569381}
[modify] https://crrev.com/c0dbb3daf5f5639ddd98f8601c9578d1b85d2d23/third_party/WebKit/LayoutTests/TestExpectations

raphael@ could you take a look, I will be away for 2.5 weeks.

FAIL AbsoluteOrientationSensor: sensor is not suspended when focus traverses from to same-origin frame assert_true: Not expecting event, but got reading event expected true got false

This looks like assertion from event watcher. I think it should be easy to fix, e.g., stop sensor right after verification that events are fired. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5ec019bba57bcbd016d5af8a0b096d7213662ff7

commit 5ec019bba57bcbd016d5af8a0b096d7213662ff7
Author: Xianzhu Wang <wangxianzhu@chromium.org>
Date: Sun Jun 24 00:02:53 2018

Mark external/wpt/magnetometer/Magnetometer-iframe-access.https.html flaky

Also removed the stale expectation files on mac

TBR=thakis@chromium.org

Bug:  855222 
Change-Id: Iaaaebfcb5dc00c0d1c42f3a2ecbb5bbfcbbbf57c
Reviewed-on: https://chromium-review.googlesource.com/1112949
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569918}
[modify] https://crrev.com/5ec019bba57bcbd016d5af8a0b096d7213662ff7/third_party/WebKit/LayoutTests/TestExpectations
[delete] https://crrev.com/901eb2a19f2408f92f1c571a42e526f02b35d43e/third_party/WebKit/LayoutTests/platform/mac-mac10.10/external/wpt/magnetometer/Magnetometer-iframe-access.https-expected.txt
[delete] https://crrev.com/901eb2a19f2408f92f1c571a42e526f02b35d43e/third_party/WebKit/LayoutTests/platform/mac-mac10.11/external/wpt/magnetometer/Magnetometer-iframe-access.https-expected.txt
[delete] https://crrev.com/901eb2a19f2408f92f1c571a42e526f02b35d43e/third_party/WebKit/LayoutTests/platform/mac-mac10.12/external/wpt/magnetometer/Magnetometer-iframe-access.https-expected.txt
[delete] https://crrev.com/901eb2a19f2408f92f1c571a42e526f02b35d43e/third_party/WebKit/LayoutTests/platform/mac-retina/external/wpt/magnetometer/Magnetometer-iframe-access.https-expected.txt
[delete] https://crrev.com/901eb2a19f2408f92f1c571a42e526f02b35d43e/third_party/WebKit/LayoutTests/platform/mac/external/wpt/magnetometer/Magnetometer-iframe-access.https-expected.txt

I'll be partly-away this week due to travel, but I'll start looking at the bug.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6829d566966918236ca17eeb5c41e4eeb6b58dbc

commit 6829d566966918236ca17eeb5c41e4eeb6b58dbc
Author: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Date: Fri Jul 06 20:46:30 2018

sensors: Fix flakiness in the same-origin access check tests

Commit f73dfaffe ("[sensors] Check that sensor frame and focused frame of
same origin") added a few same-origin access check tests for sensors in
generic-sensor-iframe-tests.sub.js.

The test that checks that a sensor is not suspended when focus changes to
another same-origin frame was flaky though, especially on the Mac bots.

The actual fix is a one-liner: we were missing a call to Sensor.stop() so
that the sensor in the top-level document wouldn't continue to push
'reading' events to our EventWatcher while we were waiting for the
"is_sensor_suspended" command to be processed in iframe_sensor_handler.html.

I'm also taking the opportunity to make a few other minor improvements:
* Fix a few typos in the comments, and improve the comment explaining why we
  can end up sending more "reading" events than originally expected.
* Create the sensor belonging to the top-level document with a higher
  frequency than the default 5Hz. This makes it a lot easier to reproduce
  the error we were having and will hopefully make the test consistently
  fail in the future instead of being flaky should another related bug
  occur.
* Make the EventWatcher instances we create also watch for "error" events;
  if an error event ever gets sent, the test should now fail instead of just
  timing out waiting for a "reading" event that is never delivered.

Bug:  855222 ,  857520 
Change-Id: I945bb19d74e608089aa9aee82a4e74e05fae37ae
Reviewed-on: https://chromium-review.googlesource.com/1127048
Commit-Queue: Raphael Kubo da Costa (CET) <raphael.kubo.da.costa@intel.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573062}
[modify] https://crrev.com/6829d566966918236ca17eeb5c41e4eeb6b58dbc/third_party/WebKit/LayoutTests/TestExpectations
[modify] https://crrev.com/6829d566966918236ca17eeb5c41e4eeb6b58dbc/third_party/WebKit/LayoutTests/external/wpt/generic-sensor/generic-sensor-iframe-tests.sub.js
[delete] https://crrev.com/5245a2a060f4e6b0ce1e2913de8da57b392f8263/third_party/WebKit/LayoutTests/platform/mac-mac10.10/external/wpt/accelerometer/Accelerometer-iframe-access.https-expected.txt
[delete] https://crrev.com/5245a2a060f4e6b0ce1e2913de8da57b392f8263/third_party/WebKit/LayoutTests/platform/mac-mac10.11/external/wpt/orientation-sensor/AbsoluteOrientationSensor-iframe-access.https-expected.txt
[delete] https://crrev.com/5245a2a060f4e6b0ce1e2913de8da57b392f8263/third_party/WebKit/LayoutTests/platform/mac-mac10.12/external/wpt/accelerometer/Accelerometer-iframe-access.https-expected.txt
[delete] https://crrev.com/5245a2a060f4e6b0ce1e2913de8da57b392f8263/third_party/WebKit/LayoutTests/platform/mac-mac10.12/external/wpt/orientation-sensor/AbsoluteOrientationSensor-iframe-access.https-expected.txt
[delete] https://crrev.com/5245a2a060f4e6b0ce1e2913de8da57b392f8263/third_party/WebKit/LayoutTests/platform/mac-retina/external/wpt/accelerometer/Accelerometer-iframe-access.https-expected.txt
[delete] https://crrev.com/5245a2a060f4e6b0ce1e2913de8da57b392f8263/third_party/WebKit/LayoutTests/platform/mac/external/wpt/accelerometer/Accelerometer-iframe-access.https-expected.txt
[delete] https://crrev.com/5245a2a060f4e6b0ce1e2913de8da57b392f8263/third_party/WebKit/LayoutTests/platform/win7/external/wpt/accelerometer/Accelerometer-iframe-access.https-expected.txt