startup is not the issue in any of those cases. all three exhibit timeouts in test execution & quite a few failures.

I gave startup as an example of slowness. All the tests seems to run more slowly as well. The test failures could be also due to timeouts, I think.

Actually I was wrong, first few tests have usual speed.
So, looking at the first failing test, org.chromium.chrome.browser.payments.PaymentRequestContactDetailsTest#testQuickCancelAndAddContactShouldNotCrash, looks like it's stuck in:

I  134.104s run_tests_on_device(08ea61aa0075fdb1)  Still working on StartInstrumentation(08ea61aa0075fdb1, org.chromium.chrome.tests/org.chromium.base.test.BaseChromiumAndroidJUnitRunner, raw=True, extras={'org.chromium.base.test.util.Screenshooter.ScreenshotDir': '/storage/emulated/legacy/tmp-565f8564fd07', 'class': u'org.chromium.chrome.browser.payments.PaymentRequestContactDetailsTest#testQuickCancelAndAddContactShouldNotCrash', 'org.chromium.base.test.ScreenshotOnFailureStatement.ScreenshotFile': '/storage/emulated/legacy/temp_file-a44288a9cf49e.png'}, timeout=180, retries=0)

Looking at logcat https://luci-logdog.appspot.com/v/?s=chromium%2Fandroid%2Fswarming%2Flogcats%2F3d1274824b516211%2F%2B%2Flogcat_logcat_org.chromium.chrome.browser.payments.PaymentRequestContactDetailsTest.testQuickCancelAndAddContactShouldNotCrash_20180424T215200-UTC_08ea61aa0075fdb1
there are a lot of
04-24 21:52:36.759  6201  6201 I Choreographer: Skipped 119 frames!  The application may be doing too much work on its main thread.

These do not appear in a passing run, for example
https://luci-logdog.appspot.com/v/?s=chromium%2Fandroid%2Fswarming%2Flogcats%2F3d1303e3236c1611%2F%2B%2Flogcat_logcat_org.chromium.chrome.browser.payments.PaymentRequestContactDetailsTest.testQuickCancelAndAddContactShouldNotCrash_20180425T003454-UTC_01ab703303301a78

Was something perhaps reverted? Looks like the tests have mostly stabilized on this bot.
https://ci.chromium.org/buildbot/tryserver.chromium.android/linux_android_rel_ng/?limit=200

This is quite rare, but still happening:
https://ci.chromium.org/buildbot/tryserver.chromium.android/linux_android_rel_ng/538086
https://ci.chromium.org/buildbot/tryserver.chromium.android/linux_android_rel_ng/537959

quite rare -> downgrading priority.

Am I the only one who gets these failures?
https://ci.chromium.org/buildbot/tryserver.chromium.android/linux_android_rel_ng/550100
Timing out tests:
org.chromium.chrome.browser.customtabs.CustomTabActivityTest#testPostMessageBasic - java.lang.AssertionError: Criteria not met in allotted time.
org.chromium.chrome.browser.payments.PaymentRequestPaymentAppAndCardsTest#testNoInstrumentsInSlowBobPay - java.lang.AssertionError: Deferred startup never completed
org.chromium.chrome.browser.input.SelectPopupOtherContentViewTest#testPopupNotClosedByOtherContentView - java.lang.AssertionError: Deferred startup never completed
org.chromium.chrome.browser.preferences.password.SavePasswordsPreferencesTest#testExportCancelOnError - android.support.test.espresso.NoMatchingViewException: No views in hierarchy found matching: with string from resource id: <2131887238>[save_password_preferences_export_action_title] value: Export passwords…
org.chromium.chrome.browser.preferences.password.SavePasswordsPreferencesTest#testExportMenuItemNoLock - android.support.test.espresso.NoMatchingViewException: No views in hierarchy found matching: with string from resource id: <2131887238>[save_password_preferences_export_action_title] value: Export passwords…
org.chromium.chrome.browser.payments.PaymentRequestDynamicShippingSingleAddressTest#testQuickCloseAndAddAddressShouldNotCrash - java.util.concurrent.TimeoutException: waitForCallback timed out!
org.chromium.chrome.browser.preferences.autofill.AutofillProfilesFragmentTest#testKeyboardShownOnDpadCenter - java.lang.AssertionError: Keyboard was not shown

Not the only one. Example:
https://ci.chromium.org/p/chromium/builders/luci.chromium.try/android-kitkat-arm-rel/3572

failing chrome_public_apk shard:
https://chromium-swarm.appspot.com/task?id=3ddb4bb5679b4110&refresh=10&show_raw=1

Stack trace:

I  793.804s run_tests_on_device(08ea61aa0075fdb1)  detected failure in org.chromium.chrome.browser.payments.PaymentRequestNameTest#testAddInvalidNameAndCancel. raw output:
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    INSTRUMENTATION_STATUS: numtests=1
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    INSTRUMENTATION_STATUS: stream=
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    org.chromium.chrome.browser.payments.PaymentRequestNameTest:
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    INSTRUMENTATION_STATUS: id=AndroidJUnitRunner
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    INSTRUMENTATION_STATUS: test=testAddInvalidNameAndCancel
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    INSTRUMENTATION_STATUS: class=org.chromium.chrome.browser.payments.PaymentRequestNameTest
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    INSTRUMENTATION_STATUS: current=1
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    INSTRUMENTATION_STATUS_CODE: 1
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    INSTRUMENTATION_STATUS: numtests=1
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    INSTRUMENTATION_STATUS: stream=
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    Error in testAddInvalidNameAndCancel(org.chromium.chrome.browser.payments.PaymentRequestNameTest):
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    java.lang.AssertionError: Deferred startup never completed
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.Assert.fail(Assert.java:88)
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.Assert.assertTrue(Assert.java:41)
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.content.browser.test.util.CriteriaHelper.pollInstrumentationThread(CriteriaHelper.java:93)
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.content.browser.test.util.CriteriaHelper.pollUiThread(CriteriaHelper.java:172)
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.content.browser.test.util.CriteriaHelper.pollUiThread(CriteriaHelper.java:211)
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.content.browser.test.util.CriteriaHelper.pollUiThread(CriteriaHelper.java:223)
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.chrome.test.ChromeActivityTestRule.startMainActivityFromIntent(ChromeActivityTestRule.java:425)
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.chrome.test.ChromeActivityTestRule.startMainActivityWithURL(ChromeActivityTestRule.java:379)
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.chrome.browser.payments.PaymentRequestTestRule.startMainActivity(PaymentRequestTestRule.java:155)
I  793.804s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.chrome.browser.payments.PaymentRequestTestRule$6.evaluate(PaymentRequestTestRule.java:1094)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.chrome.test.ChromeActivityTestRule$1.evaluate(ChromeActivityTestRule.java:115)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at android.support.test.internal.statement.UiThreadStatement.evaluate(UiThreadStatement.java:55)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at android.support.test.rule.ActivityTestRule$ActivityStatement.evaluate(ActivityTestRule.java:270)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.rules.ExternalResource$1.evaluate(ExternalResource.java:48)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.rules.RunRules.evaluate(RunRules.java:20)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.base.test.BaseJUnit4ClassRunner.runChild(BaseJUnit4ClassRunner.java:238)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.base.test.BaseJUnit4ClassRunner.runChild(BaseJUnit4ClassRunner.java:49)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.chromium.base.test.BaseJUnit4ClassRunner.run(BaseJUnit4ClassRunner.java:221)
I  793.805s run_tests_on_device(08ea61aa0075fdb1)    	at org.junit.runners.Suite.runChild(Suite.java:128)


Not sure whether this is specific to PaymentRequest.

This issue has an owner, a component and a priority, but is still listed as untriaged or unconfirmed. By definition, this bug is triaged. Changing status to "assigned". Please reach out to me if you disagree with how I've done this.