Central as early beta simulation: https://treeherder.mozilla.org/#/jobs?repo=try&resultStatus=success%2Ctestfailed%2Cbusted%2Cexception&revision=a382df6299c368321b5a306cdb411ae3c7cfa785&searchStr=wpt9&selectedJob=248537801

Failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=248537801&repo=try&lineNumber=63167

12:44:39 INFO - TEST-START | /webvr/webvr-supported-by-feature-policy.html
12:44:39 INFO - Clearing pref dom.security.featurePolicy.enabled
12:44:39 INFO - PID 9832 | Exiting due to channel error.
12:44:39 INFO - PID 9832 | [GPU 8768, Main Thread] WARNING: Shutting down GPU process early due to a crash!: file z:/build/build/src/gfx/ipc/GPUParent.cpp, line 484
12:44:39 INFO - PID 9832 | [GPU Exiting due to channel error.
12:44:39 CRITICAL - Traceback (most recent call last):
12:44:39 CRITICAL - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\testrunner.py", line 115, in run_test
12:44:39 CRITICAL - return self.executor.run_test(test)
12:44:39 CRITICAL - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\executors\base.py", line 190, in run_test
12:44:39 CRITICAL - self.on_environment_change(test.environment)
12:44:39 CRITICAL - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\executors\executormarionette.py", line 671, in on_environment_change
12:44:39 CRITICAL - self.protocol.on_environment_change(self.last_environment, new_environment)
12:44:39 CRITICAL - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\executors\executormarionette.py", line 538, in on_environment_change
12:44:39 CRITICAL - self.prefs.clear(name)
12:44:39 CRITICAL - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\executors\executormarionette.py", line 274, in clear
12:44:39 CRITICAL - self.marionette.execute_script(script)
12:44:39 CRITICAL - File "c:\mozilla-build\python\Lib\contextlib.py", line 35, in exit
12:44:39 CRITICAL - self.gen.throw(type, value, traceback)
12:44:39 CRITICAL - File "Z:\task_1558956757\build\venv\lib\site-packages\marionette_driver\marionette.py", line 1332, in using_context
12:44:39 CRITICAL - self.set_context(scope)
12:44:39 CRITICAL - File "Z:\task_1558956757\build\venv\lib\site-packages\marionette_driver\marionette.py", line 1309, in set_context
12:44:39 CRITICAL - {"value": context})
12:44:39 CRITICAL - File "Z:\task_1558956757\build\venv\lib\site-packages\marionette_driver\decorators.py", line 26, in _
12:44:39 CRITICAL - return func(*args, **kwargs)
12:44:39 CRITICAL - File "Z:\task_1558956757\build\venv\lib\site-packages\marionette_driver\marionette.py", line 587, in _send_message
12:44:39 CRITICAL - raise errors.InvalidSessionIdException("Please start a session")
12:44:39 CRITICAL - InvalidSessionIdException: Please start a session
12:44:39 CRITICAL -
12:44:39 ERROR - Error running command run_test with arguments (<wptrunner.wpttest.TestharnessTest /webvr/webvr-supported-by-feature-policy.html>,):
12:44:39 ERROR - Traceback (most recent call last):
12:44:39 ERROR - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\testrunner.py", line 98, in run
12:44:39 ERROR - rv = commandscommand
12:44:39 ERROR - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\testrunner.py", line 115, in run_test
12:44:39 ERROR - return self.executor.run_test(test)
12:44:39 ERROR - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\executors\base.py", line 190, in run_test
12:44:39 ERROR - self.on_environment_change(test.environment)
12:44:39 ERROR - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\executors\executormarionette.py", line 671, in on_environment_change
12:44:39 ERROR - self.protocol.on_environment_change(self.last_environment, new_environment)
12:44:39 ERROR - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\executors\executormarionette.py", line 538, in on_environment_change
12:44:39 ERROR - self.prefs.clear(name)
12:44:39 ERROR - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\executors\executormarionette.py", line 274, in clear
12:44:39 ERROR - self.marionette.execute_script(script)
12:44:39 ERROR - File "c:\mozilla-build\python\Lib\contextlib.py", line 35, in exit
12:44:39 ERROR - self.gen.throw(type, value, traceback)
12:44:39 ERROR - File "Z:\task_1558956757\build\venv\lib\site-packages\marionette_driver\marionette.py", line 1332, in using_context
12:44:39 ERROR - self.set_context(scope)
12:44:39 ERROR - File "Z:\task_1558956757\build\venv\lib\site-packages\marionette_driver\marionette.py", line 1309, in set_context
12:44:39 ERROR - {"value": context})
12:44:39 ERROR - File "Z:\task_1558956757\build\venv\lib\site-packages\marionette_driver\decorators.py", line 26, in _
12:44:39 ERROR - return func(*args, **kwargs)
12:44:39 ERROR - File "Z:\task_1558956757\build\venv\lib\site-packages\marionette_driver\marionette.py", line 587, in _send_message
12:44:39 ERROR - raise errors.InvalidSessionIdException("Please start a session")
12:44:39 ERROR - InvalidSessionIdException: Please start a session
12:44:39 ERROR -
12:44:39 ERROR - Traceback (most recent call last):
12:44:39 ERROR - File "Z:\task_1558956757\build\tests\web-platform\tests\tools\wptrunner\wptrunner\testrunner.py", line 371, in run

Seems to be caused by the changes in either Bug 1554438 or Bug 1550422

Likely the same as bug 1554597

Confirmed to be a duplicate.

Try with the fix reverted shows error
https://treeherder.mozilla.org/#/jobs?repo=try&selectedJob=248689794&revision=37f2444da769a665ada6d32bde2c000754c4bc25

Try with the fix:
https://treeherder.mozilla.org/#/jobs?repo=try&selectedJob=248689794&revision=9e86350bcc391f4149f7d55bdc1f270da72bec76
No error in wpt