Android: Add assert in EarlyTraceEventTest#testCanRecordEventUsingTryWith.

This test has been flaky. The additional assert may shed some light onto
what's going on.

TBR: yfriedman@chromium.org
Bug: 930174
Change-Id: Ifdc99b3c49f7d827818ca7ff8dbea12b856d2101
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1546107Reviewed-by: Matthew Cary <mattcary@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Cr-Commit-Position: refs/heads/master@{#646293}

base/android/javatests/src/org/chromium/base/EarlyTraceEventTest.java

@@ -105,6 +105,7 @@ public class EarlyTraceEventTest {
         EarlyTraceEvent.enable();
         long myThreadId = Process.myTid();
         long beforeNanos = Event.elapsedRealtimeNanos();
+        Assert.assertTrue(EarlyTraceEvent.sPendingEventByKey.isEmpty());
         try (TraceEvent e = TraceEvent.scoped(EVENT_NAME)) {
             // Required comment to pass presubmit checks.
         }