Fix more swarming test failures by using fake clock.

webrtc/p2p/base/port.cc

Index: webrtc/p2p/base/port.cc
diff --git a/webrtc/p2p/base/port.cc b/webrtc/p2p/base/port.cc
index 8742d0f9e2c15136b22340ffe53dde7c2fb1b5af..b9ead32b543525ae571e46b72d1ab392c2d5afda 100644
--- a/webrtc/p2p/base/port.cc
+++ b/webrtc/p2p/base/port.cc
@@ -925,7 +925,8 @@ void Connection::set_write_state(WriteState value) {
 }
 
 void Connection::UpdateReceiving(int64_t now) {
-  bool receiving = now <= last_received() + receiving_timeout_;
+  bool receiving =
+      last_received() > 0 && now <= last_received() + receiving_timeout_;
   if (receiving_ == receiving) {
     return;
   }