Many "SignedIn" tests have been failing on Marshmallow Tablet Tester since:
https://build.chromium.org/p/chromium.android/builders/Marshmallow%20Tablet%20Tester/builds/3222

These include tests in:
- org.chromium.chrome.test.util.ChromeSigninUtilsTest
- org.chromium.chrome.test.ParametersOnMultiTest
- org.chromium.chrome.test.util.parameters.SigninParametersTest

The error message reads, e.g.:

C 1098.252s Main  [FAIL] org.chromium.chrome.test.util.parameters.SigninParametersTest#testActivityIsNotSignedInOnAppOrFakeOSorGoogleOS:
C 1098.252s Main  java.lang.SecurityException: org.chromium.chrome.tests from uid 10085 not allowed to perform GET_ACCOUNTS
C 1098.252s Main  	at android.os.Parcel.readException(Parcel.java:1599)
C 1098.252s Main  	at android.os.Parcel.readException(Parcel.java:1552)
C 1098.252s Main  	at android.accounts.IAccountManager$Stub$Proxy.getAccountsAsUser(IAccountManager.java:816)
C 1098.252s Main  	at android.accounts.AccountManager.getAccountsByTypeAsUser(AccountManager.java:526)
C 1098.252s Main  	at android.accounts.AccountManager.getAccountsByType(AccountManager.java:520)
C 1098.252s Main  	at org.chromium.chrome.test.util.ChromeSigninUtils.isExistingGoogleAccountOnOs(ChromeSigninUtils.java:148)
C 1098.252s Main  	at org.chromium.chrome.test.util.parameters.AddGoogleAccountToOsParameter.isSignedIn(AddGoogleAccountToOsParameter.java:54)
C 1098.252s Main  	at org.chromium.chrome.test.util.parameters.SigninParametersTest.testActivityIsNotSignedInOnAppOrFakeOSorGoogleOS(SigninParametersTest.java:50)
C 1098.252s Main  	at android.test.InstrumentationTestCase.runMethod(InstrumentationTestCase.java:214)
C 1098.252s Main  	at android.test.InstrumentationTestCase.runTest(InstrumentationTestCase.java:199)
C 1098.252s Main  	at android.test.ActivityInstrumentationTestCase2.runTest(ActivityInstrumentationTestCase2.java:192)
C 1098.252s Main  	at org.chromium.chrome.test.ChromeActivityTestCaseBase.runTest(ChromeActivityTestCaseBase.java:793)
C 1098.252s Main  	at org.chromium.base.test.BaseTestResult.runParameterized(BaseTestResult.java:161)
C 1098.252s Main  	at org.chromium.base.test.BaseTestResult.run(BaseTestResult.java:124)
C 1098.252s Main  	at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:191)
C 1098.252s Main  	at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:176)
C 1098.252s Main  	at android.test.InstrumentationTestRunner.onStart(InstrumentationTestRunner.java:555)
C 1098.252s Main  	at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1879)