Update VirtualSocketServerTest to use a fake clock.

webrtc/base/thread.cc

Index: webrtc/base/thread.cc
diff --git a/webrtc/base/thread.cc b/webrtc/base/thread.cc
index 1be5196c7dffbf8325b679c1504f19df1eb7f2b3..9174cd1bd6de531f80d6a200bf3c4afd4498c521 100644
--- a/webrtc/base/thread.cc
+++ b/webrtc/base/thread.cc
@@ -471,6 +471,11 @@ void Thread::Clear(MessageHandler* phandler,
 // Note that these methods have a separate implementation for mac and ios
 // defined in webrtc/base/thread_darwin.mm.
 bool Thread::ProcessMessages(int cmsLoop) {
+  // Using ProcessMessages with a custom clock for testing and a time greater
+  // than 0 doesn't work, since it's not guaranteed to advance the custom
+  // clock's time, and may get stuck in an infinite loop.
+  RTC_DCHECK(GetClockForTesting() == nullptr || cmsLoop == 0 ||
+             cmsLoop == kForever);
   int64_t msEnd = (kForever == cmsLoop) ? 0 : TimeAfter(cmsLoop);
   int cmsNext = cmsLoop;