Improving diagnostics when Launcher dies during a gesture

Instead of crashing upon getting uninitialized event sequence, we show a
meaningful message.

Bug: 159921830
Change-Id: Ie42039b39a453c60bd5df3e54058d582137bba06

ext_tests/src/com/android/launcher3/testing/DebugTestInformationHandler.java

@@ -164,6 +164,12 @@ public class DebugTestInformationHandler extends TestInformationHandler {
             }
 
             case TestProtocol.REQUEST_GET_TEST_EVENTS: {
+                if (sEvents == null) {
+                    // sEvents can be null if Launcher died and restarted after
+                    // REQUEST_START_EVENT_LOGGING.
+                    return response;
+                }
+
                 synchronized (sEvents) {
                     response.putStringArrayList(
                             TestProtocol.TEST_INFO_RESPONSE_FIELD, new ArrayList<>(sEvents));