Failed to run wpt test on chrome_android.

Hi,

First, thank you very much for your time to read my questions. My steps are
as below:
1) I git cloned the latest web-platform-tests to my
workstation(Ubuntu16.04).
2) Downloaded the chromium source code for android(71.0.3546.0) and built
out a "ChromePublic.apk".
3) Followed the instructions in "docs/_running-tests/chrome_android.md".

Then I plugged in the usb cable to an android phone(already rooted and its
/etc/hosts has been modified like suggested), adb install the
ChromePublic.apk, then run:
"./wpt run chrome_android wake-lock" (choose wake-lock just because it
contains fewer test cases)

It failed with logs:

*./wpt run chrome_android wake-lockUsing webdriver binary
/home/wade/heke/wpt/wpt/_venv/bin/chromedriver 0:02.63 INFO Updating test
manifest /home/wade/heke/wpt/wpt/MANIFEST.json 0:02.66 INFO STDOUT:
INFO:manifest:Skipping manifest download because existing file is recent
0:07.80 INFO STDOUT: INFO:manifest:Updating manifest 1:24.30 INFO STDOUT:
DEBUG:manifest:Opening manifest at /home/wade/heke/wpt/wpt/MANIFEST.json
1:31.81 INFO Using 1 client processes 1:31.95 INFO Starting http server on
web-platform.test:8000 1:31.96 INFO Starting http server on
web-platform.test:8001 1:32.04 INFO Starting https server on
web-platform.test:8443 1:32.49 SUITE_START: web-platform-test - running 15
tests 1:32.49 INFO Running reftest tests 1:32.71 INFO No reftest tests to
run 1:32.71 INFO Running wdspec tests 1:32.72 INFO No wdspec tests to run
1:32.72 INFO Running testharness tests 1:32.75 INFO adb wait-for-device
1:32.88 INFO adb forward --remove-all 1:32.94 INFO adb reverse --remove-all
1:33.03 INFO adb reverse tcp:8000 tcp:8000 1:33.13 INFO adb reverse
tcp:8001 tcp:8001 1:33.23 INFO adb reverse tcp:8888 tcp:8888 1:33.33 INFO
adb reverse tcp:8889 tcp:8889 1:33.43 INFO adb reverse tcp:8443 tcp:8443
1:33.68 pid:20561 Full command:
/home/wade/heke/wpt/wpt/_venv/bin/chromedriver --port=4444
--url-base=/pid:20561 Starting ChromeDriver 2.41.578700
(2f1ed5f9343c13f73144538f15c00b370eda6706) on port 4444 1:33.68 pid:20561
Only local connections are allowed. 1:34.11 INFO Starting runner 1:35.21
WARNING Failed to start protocol connection 1:35.21 ERROR Traceback (most
recent call last):  File
"/home/wade/heke/wpt/wpt/tools/wptrunner/wptrunner/executors/protocol.py",
line 47, in setup    self.connect()  File
"/home/wade/heke/wpt/wpt/tools/wptrunner/wptrunner/executors/executorselenium.py",
line 180, in connect    desired_capabilities=self.capabilities)  File
"/home/wade/heke/wpt/wpt/_venv/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.py",
line 156, in __init__    self.start_session(capabilities, browser_profile)
 File
"/home/wade/heke/wpt/wpt/_venv/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.py",
line 251, in start_session    response = self.execute(Command.NEW_SESSION,
parameters)  File
"/home/wade/heke/wpt/wpt/_venv/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.py",
line 320, in execute    self.error_handler.check_response(response)  File
"/home/wade/heke/wpt/wpt/_venv/lib/python2.7/site-packages/selenium/webdriver/remote/errorhandler.py",
line 242, in check_response    raise exception_class(message, screen,
stacktrace)WebDriverException: Message: unknown error:
com.google.android.apps.chrome is not installed on device 00447583  (Driver
info: chromedriver=2.41.578700
(2f1ed5f9343c13f73144538f15c00b370eda6706),platform=Linux 4.4.0-112-generic
x86_64)*

I see something went wrong from logs:

*"WARNING Failed to start protocol connection" and *

*"WebDriverException: Message: unknown error:
com.google.android.apps.chrome is not installed on device 00447583"*
I also downloaded a Chrome apk(version 68) from some app store and tried
again, but some error happened.
Could some experts give some hints on this? thanks very much!

Ke