The 100ms timeout is too short.  If a garbage collection pass takes place it can take more than 100ms.  Here's an example logcat:

09-14 02:00:43.275  5386  5423 I TestRunner: started: testEmptyGetCertVerifierData(org.chromium.net.CronetUrlRequestContextTest)
09-14 02:00:43.281  5386  5386 I MonitoringInstr: Activities that are still in CREATED to STOPPED: 0
09-14 02:00:43.304  5386  5423 I cr_TestServer: Waiting for EmbeddedTestServer service connection.
09-14 02:00:43.309  5386  5423 I cr_TestServer: Still waiting for EmbeddedTestServer service connection.
09-14 02:00:43.309  5386  5423 I cr_TestServer: EmbeddedTestServer service connected.
09-14 02:00:43.358  5386  5423 I cr_CronetLibraryLoader: Cronet version: 61.0.3163.81, arch: i686
09-14 02:00:43.566  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.589  5386  5423 I art     : Explicit concurrent mark sweep GC freed 26572(2043KB) AllocSpace objects, 6(152KB) LOS objects, 40% free, 2MB/4MB, paused 626us total 22.981ms
09-14 02:00:43.597  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.602  5402  5421 D NativeLibraryUtils: Install completed successfully. count=12 extracted=0
09-14 02:00:43.612  5386  5423 I art     : Explicit concurrent mark sweep GC freed 739(31KB) AllocSpace objects, 0(0B) LOS objects, 39% free, 2MB/4MB, paused 733us total 14.919ms
09-14 02:00:43.613  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.627  5386  5423 I art     : Explicit concurrent mark sweep GC freed 5(128B) AllocSpace objects, 0(0B) LOS objects, 39% free, 2MB/4MB, paused 923us total 13.977ms
09-14 02:00:43.627  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.644  5386  5423 I art     : Explicit concurrent mark sweep GC freed 5(128B) AllocSpace objects, 0(0B) LOS objects, 39% free, 2MB/4MB, paused 675us total 16.202ms
09-14 02:00:43.645  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.663  5386  5423 I art     : Explicit concurrent mark sweep GC freed 5(128B) AllocSpace objects, 0(0B) LOS objects, 39% free, 2MB/4MB, paused 724us total 17.264ms
09-14 02:00:43.663  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.685  5386  5423 I art     : Explicit concurrent mark sweep GC freed 5(128B) AllocSpace objects, 0(0B) LOS objects, 39% free, 2MB/4MB, paused 710us total 21.231ms
09-14 02:00:43.685  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.701  5386  5423 I art     : Explicit concurrent mark sweep GC freed 5(128B) AllocSpace objects, 0(0B) LOS objects, 39% free, 2MB/4MB, paused 758us total 15.965ms
09-14 02:00:43.704  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.720  5386  5423 I art     : Explicit concurrent mark sweep GC freed 5(128B) AllocSpace objects, 0(0B) LOS objects, 39% free, 2MB/4MB, paused 654us total 15.221ms
09-14 02:00:43.720  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.736  5386  5423 I art     : Explicit concurrent mark sweep GC freed 5(128B) AllocSpace objects, 0(0B) LOS objects, 39% free, 2MB/4MB, paused 679us total 14.864ms
09-14 02:00:43.736  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.754  5386  5423 I art     : Explicit concurrent mark sweep GC freed 5(128B) AllocSpace objects, 0(0B) LOS objects, 39% free, 2MB/4MB, paused 605us total 18.257ms
09-14 02:00:43.756  5386  5423 I art     : Starting a blocking GC Explicit
09-14 02:00:43.770  5386  5423 I art     : Explicit concurrent mark sweep GC freed 5(128B) AllocSpace objects, 0(0B) LOS objects, 39% free, 2MB/4MB, paused 645us total 13.482ms
09-14 02:00:43.773  5386  5423 I TestRunner: failed: testEmptyGetCertVerifierData(org.chromium.net.CronetUrlRequestContextTest)
09-14 02:00:43.773  5386  5423 I TestRunner: ----- begin exception -----
09-14 02:00:43.774  5386  5423 I TestRunner: java.lang.Throwable: CronetTestBase#runTest failed.
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.chromium.net.CronetTestBase.runTest(CronetTestBase.java:200)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at junit.framework.TestCase.runBare(TestCase.java:134)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at junit.framework.TestResult$1.protect(TestResult.java:115)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at android.support.test.internal.runner.junit3.AndroidTestResult.runProtected(AndroidTestResult.java:77)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at junit.framework.TestResult.run(TestResult.java:118)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at android.support.test.internal.runner.junit3.AndroidTestResult.run(AndroidTestResult.java:55)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at junit.framework.TestCase.run(TestCase.java:124)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at android.support.test.internal.runner.junit3.NonLeakyTestSuite$NonLeakyTest.run(NonLeakyTestSuite.java:63)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at junit.framework.TestSuite.runTest(TestSuite.java:243)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at junit.framework.TestSuite.run(TestSuite.java:238)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at android.support.test.internal.runner.junit3.DelegatingTestSuite.run(DelegatingTestSuite.java:103)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at android.support.test.internal.runner.junit3.AndroidTestSuite.run(AndroidTestSuite.java:73)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at android.support.test.internal.runner.junit3.JUnit38ClassRunner.run(JUnit38ClassRunner.java:119)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.junit.runners.Suite.runChild(Suite.java:127)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.junit.runners.Suite.runChild(Suite.java:26)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:240)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:65)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:238)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:55)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:231)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.junit.runners.ParentRunner.run(ParentRunner.java:316)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.junit.runner.JUnitCore.run(JUnitCore.java:138)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at android.support.test.internal.runner.TestExecutor.execute(TestExecutor.java:58)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at
09-14 02:00:43.774  5386  5423 I TestRunner: 	at
09-14 02:00:43.774  5386  5423 I TestRunner: 	at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1932)
09-14 02:00:43.774  5386  5423 I TestRunner: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.chromium.net.CronetUrlRequestContextTest.testEmptyGetCertVerifierData(CronetUrlRequestContextTest.java:1066)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at java.lang.reflect.Method.invoke(Native Method)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at junit.framework.TestCase.runTest(TestCase.java:168)
09-14 02:00:43.774  5386  5423 I TestRunner: 	at org.chromium.net.CronetTestBase.runTest(CronetTestBase.java:186)
09-14 02:00:43.774  5386  5423 I TestRunner: 	... 26 more
09-14 02:00:43.774  5386  5423 I TestRunner: ----- end exception -----
09-14 02:00:43.777  5386  5423 I TestRunner: finished: testEmptyGetCertVerifierData(org.chromium.net.CronetUrlRequestContextTest)