Add default constructor for rtc::Event

Bug: webrtc:9962
Change-Id: Icaa91e657e6881fcb1553f354c07866109a0ea68
Reviewed-on: https://webrtc-review.googlesource.com/c/109500
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25535}

modules/audio_processing/aec_dump/aec_dump_impl.cc

@@ -65,7 +65,7 @@ AecDumpImpl::AecDumpImpl(std::unique_ptr<FileWrapper> debug_file,
 
 AecDumpImpl::~AecDumpImpl() {
   // Block until all tasks have finished running.
-  rtc::Event thread_sync_event(false /* manual_reset */, false);
+  rtc::Event thread_sync_event;
   worker_queue_->PostTask([&thread_sync_event] { thread_sync_event.Set(); });
   // Wait until the event has been signaled with .Set(). By then all
   // pending tasks will have finished.

modules/audio_processing/audio_processing_impl_locking_unittest.cc

@@ -487,10 +487,7 @@ void PopulateAudioFrame(AudioFrame* frame,
 }
 
 AudioProcessingImplLockTest::AudioProcessingImplLockTest()
-    : test_complete_(false, false),
-      render_call_event_(false, false),
-      capture_call_event_(false, false),
-      render_thread_(RenderProcessorThreadFunc, this, "render"),
+    : render_thread_(RenderProcessorThreadFunc, this, "render"),
       capture_thread_(CaptureProcessorThreadFunc, this, "capture"),
       stats_thread_(StatsProcessorThreadFunc, this, "stats"),
       apm_(AudioProcessingBuilder().Create()),

modules/audio_processing/audio_processing_performance_unittest.cc

@@ -391,8 +391,7 @@ class TimedThreadApiProcessor {
 class CallSimulator : public ::testing::TestWithParam<SimulationConfig> {
  public:
   CallSimulator()
-      : test_complete_(false, false),
-        render_thread_(
+      : render_thread_(
             new rtc::PlatformThread(RenderProcessorThreadFunc, this, "render")),
         capture_thread_(new rtc::PlatformThread(CaptureProcessorThreadFunc,
                                                 this,