Fix errorprone errors.

In order to enable errorprone [1] we have to fix this finding.

third_party/errorprone has been recently enabled in Chromium and in
order to unblock the Chromium Roll we have to fix these errors. 

[1] - https://cs.chromium.org/chromium/src/third_party/errorprone/

Bug: webrtc:8390
Change-Id: Ic737def5ae2a8c6ad1216d9b485af59987fe511c
Tbr: magjed@webrtc.org
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/9161
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20273}

examples/androidjunit/src/org/appspot/apprtc/TCPChannelClientTest.java

@@ -101,6 +101,7 @@ public class TCPChannelClientTest {
   // Disabled because it fails when IPv6 is not supported on the bot.
   // TODO(ehmaldonado): Enable when bugs.webrtc.org/6437 is fixed.
   @DisabledTest
+  @SuppressWarnings("JUnit4TestNotRun")
   public void testConnectIPv6() {
     setUpIPv6Server();
     try {

sdk/android/instrumentationtests/src/org/webrtc/PeerConnectionTest.java

@@ -280,7 +280,7 @@ public class PeerConnectionTest {
     @Override
     public synchronized void onComplete(StatsReport[] reports) {
       if (--expectedOldStatsCallbacks < 0) {
-        throw new RuntimeException("Unexpected stats report: " + reports);
+        throw new RuntimeException("Unexpected stats report: " + Arrays.toString(reports));
       }
       gotStatsReports.add(reports);
     }