In all 3 cases the error log is
=== START ===
junit.framework.ComparisonFailure: expected:<[HELLOfrom_js]> but was:<[]>
	at org.chromium.android_webview.test.PostMessageTest.testMessageChannelUsingPendingPort(PostMessageTest.java:702)
	at java.lang.reflect.Method.invokeNative(Native Method)
	at android.test.InstrumentationTestCase.runMethod(InstrumentationTestCase.java:214)
	at android.test.InstrumentationTestCase.runTest(InstrumentationTestCase.java:199)
	at android.test.ActivityInstrumentationTestCase2.runTest(ActivityInstrumentationTestCase2.java:192)
	at org.chromium.base.test.BaseTestResult.runParameterized(BaseTestResult.java:161)
	at org.chromium.base.test.BaseTestResult.run(BaseTestResult.java:124)
	at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:191)
	at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:176)
	at android.test.InstrumentationTestRunner.onStart(InstrumentationTestRunner.java:554)
	at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1701)
=== END ===

I am disabling the test.

The CL is https://codereview.chromium.org/2845863004/ and it is being submitted right now.

Please have a look.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c186cf10dc3367044f9143308bc3452eff0cd22c

commit c186cf10dc3367044f9143308bc3452eff0cd22c
Author: vitaliii <vitaliii@chromium.org>
Date: Thu Apr 27 14:18:14 2017

Disable PostMessageTest#testMessageChannelUsingPendingPort because flaky

Disable org.chromium.android_webview.test.PostMessageTest#testMessageCha
nnelUsingPendingPort because it is flaky.

TBR=sgurun@chromium.org

BUG= 715960 

Review-Url: https://codereview.chromium.org/2845863004
Cr-Commit-Position: refs/heads/master@{#467667}

[modify] https://crrev.com/c186cf10dc3367044f9143308bc3452eff0cd22c/android_webview/javatests/src/org/chromium/android_webview/test/PostMessageTest.java

interesting. This is the second postmessage test that was marked as flaky, and these tests worked fine for more than a year. 

I wonder if some refactoring has anything to do with it. Darin's CL is the most major one I can think of.

looped test locally 50 times and no failures. gonna try enabling with RetryOnFailure. I guess someone check back in a couple of weeks and see if there are any flakes on the flakiness dashboard

https://chromium-review.googlesource.com/c/chromium/src/+/685281

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/dacb6d43eff1948adf3f458f2a285902aac4bdc1

commit dacb6d43eff1948adf3f458f2a285902aac4bdc1
Author: Bo Liu <boliu@chromium.org>
Date: Tue Sep 26 23:24:16 2017

aw: Enable testMessageChannelUsingPendingPort with RetryOnFailure

Can't repro failure locally, so try again on bots.

Bug:  715960 
Change-Id: I9f6393799927e45c15804a8d41cdb16e0ef4da04
Reviewed-on: https://chromium-review.googlesource.com/685281
Reviewed-by: Paul Miller <paulmiller@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504517}
[modify] https://crrev.com/dacb6d43eff1948adf3f458f2a285902aac4bdc1/android_webview/javatests/src/org/chromium/android_webview/test/PostMessageTest.java

Looks pretty good. Not a single retry flake so far: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webview_instrumentation_test_apk&tests=org.chromium.android_webview.test.PostMessageTest%23testMessageChannelUsingPendingPort

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/41147dd6d6eb10938fb002f546ad94bcb702b233

commit 41147dd6d6eb10938fb002f546ad94bcb702b233
Author: Bo Liu <boliu@chromium.org>
Date: Sun Oct 01 03:58:14 2017

aw: Remove RetryOnFailure for testMessageChannelUsingPendingPort

Looks good on cq for 3 days.

Bug:  715960 
Change-Id: I40905c5ddcb7cbb1797906ace7126a52d20c33a8
Reviewed-on: https://chromium-review.googlesource.com/693416
Reviewed-by: Paul Miller <paulmiller@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505497}
[modify] https://crrev.com/41147dd6d6eb10938fb002f546ad94bcb702b233/android_webview/javatests/src/org/chromium/android_webview/test/PostMessageTest.java