Make the default ctor of rtc::Thread, protected

webrtc/pc/test/fakeaudiocapturemodule.cc

Index: webrtc/pc/test/fakeaudiocapturemodule.cc
diff --git a/webrtc/pc/test/fakeaudiocapturemodule.cc b/webrtc/pc/test/fakeaudiocapturemodule.cc
index 4bc6e4faec69957b065349f0ee01340c857b8de1..5812d3900fce8d0fabc432334688da8096f3a448 100644
--- a/webrtc/pc/test/fakeaudiocapturemodule.cc
+++ b/webrtc/pc/test/fakeaudiocapturemodule.cc
@@ -624,7 +624,7 @@ bool FakeAudioCaptureModule::ShouldStartProcessing() {
 void FakeAudioCaptureModule::UpdateProcessing(bool start) {
   if (start) {
     if (!process_thread_) {
-      process_thread_.reset(new rtc::Thread());
+      process_thread_ = rtc::Thread::Create();
       process_thread_->Start();
     }
     process_thread_->Post(RTC_FROM_HERE, this, MSG_START_PROCESS);