The MediaAccessPermissionRequestTest tests are very flaky on Marshmallow Tablet Tester:
https://uberchromegw.corp.google.com/i/chromium.android/builders/Marshmallow%20Tablet%20Tester?numbuilds=200

Example failing runs:
https://uberchromegw.corp.google.com/i/chromium.android/builders/Marshmallow%20Tablet%20Tester/builds/4008
https://uberchromegw.corp.google.com/i/chromium.android/builders/Marshmallow%20Tablet%20Tester/builds/4011

Logs:
C 1346.158s Main  [FAIL] org.chromium.android_webview.test.MediaAccessPermissionRequestTest#testCancelPermission with {--webview-sandboxed-renderer}:
C 1346.158s Main  java.util.concurrent.TimeoutException: waitForCallback timed out!
C 1346.158s Main  	at org.chromium.content.browser.test.util.CallbackHelper.waitForCallback(CallbackHelper.java:184)
C 1346.158s Main  	at org.chromium.content.browser.test.util.CallbackHelper.waitForCallback(CallbackHelper.java:192)
C 1346.158s Main  	at org.chromium.content.browser.test.util.CallbackHelper.waitForCallback(CallbackHelper.java:198)
C 1346.158s Main  	at org.chromium.android_webview.test.MediaAccessPermissionRequestTest.testCancelPermission(MediaAccessPermissionRequestTest.java:191)
C 1346.158s Main  	at android.test.InstrumentationTestCase.runMethod(InstrumentationTestCase.java:214)
C 1346.159s Main  	at android.test.InstrumentationTestCase.runTest(InstrumentationTestCase.java:199)
C 1346.159s Main  	at android.test.ActivityInstrumentationTestCase2.runTest(ActivityInstrumentationTestCase2.java:192)
C 1346.159s Main  	at org.chromium.base.test.BaseTestResult.runParameterized(BaseTestResult.java:161)
C 1346.159s Main  	at org.chromium.base.test.BaseTestResult.run(BaseTestResult.java:124)
C 1346.159s Main  	at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:191)
C 1346.159s Main  	at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:176)
C 1346.159s Main  	at android.test.InstrumentationTestRunner.onStart(InstrumentationTestRunner.java:555)
C 1346.159s Main  	at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1879)