Seeing fairly regular failures on the flakiness dashboard: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=chrome_public_test_apk&tests=BottomSheetBackBehaviorTest%23testBackButton_backButtonOpensSheetAndShowsToolbar

This build:
https://uberchromegw.corp.google.com/i/chromium.android/builders/Marshmallow%2064%20bit%20Tester/builds/17879

Showed this error:
java.lang.AssertionError
	at org.junit.Assert.fail(Assert.java:86)
	at org.junit.Assert.assertTrue(Assert.java:41)
	at org.chromium.content.browser.test.util.CriteriaHelper.pollInstrumentationThread(CriteriaHelper.java:93)
	at org.chromium.content.browser.test.util.CriteriaHelper.pollUiThread(CriteriaHelper.java:172)
	at org.chromium.content.browser.test.util.CriteriaHelper.pollUiThread(CriteriaHelper.java:211)
	at org.chromium.content.browser.test.util.CriteriaHelper.pollUiThread(CriteriaHelper.java:223)
	at org.chromium.content.browser.test.util.CriteriaHelper.pollUiThread(CriteriaHelper.java:234)
	at org.chromium.chrome.browser.widget.bottomsheet.BottomSheetBackBehaviorTest.hideBrowserControls(BottomSheetBackBehaviorTest.java:274)
	at org.chromium.chrome.browser.widget.bottomsheet.BottomSheetBackBehaviorTest.testBackButton_backButtonOpensSheetAndShowsToolbar(BottomSheetBackBehaviorTest.java:171)
	at java.lang.reflect.Method.invoke(Native Method)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:52)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.chromium.base.test.ScreenshotOnFailureStatement.evaluate(ScreenshotOnFailureStatement.java:37)
	at org.chromium.chrome.test.ChromeActivityTestRule$1.evaluate(ChromeActivityTestRule.java:116)
	at android.support.test.internal.statement.UiThreadStatement.evaluate(UiThreadStatement.java:55)
	at android.support.test.rule.ActivityTestRule$ActivityStatement.evaluate(ActivityTestRule.java:270)
	at org.junit.rules.RunRules.evaluate(RunRules.java:20)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.chromium.base.test.BaseJUnit4ClassRunner.runChild(BaseJUnit4ClassRunner.java:184)
	at org.chromium.base.test.BaseJUnit4ClassRunner.runChild(BaseJUnit4ClassRunner.java:41)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.chromium.base.test.BaseJUnit4ClassRunner.run(BaseJUnit4ClassRunner.java:166)
	at org.junit.runners.Suite.runChild(Suite.java:128)
	at org.junit.runners.Suite.runChild(Suite.java:27)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
	at android.support.test.internal.runner.TestExecutor.execute(TestExecutor.java:59)
	at android.support.test.runner.AndroidJUnitRunner.onStart(AndroidJUnitRunner.java:262)
	at org.chromium.base.test.BaseChromiumAndroidJUnitRunner.onStart(BaseChromiumAndroidJUnitRunner.java:99)
	at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1879)
Searching for native crashes in: /b/swarming/w/it5xHrGJ/tmptOzHmh
Unknown Android release, consider passing --packed-lib.
Reading Android symbols from: /b/swarming/w/ir
Searching for Chrome symbols from within: /b/swarming/w/ir/out/Debug/lib.unstripped:/b/swarming/w/ir/out/Debug/lib:/b/swarming/w/ir/out/Debug

Matt, please take a look or reassign.