Improving the fake clock and using it to fix a flaky STUN timeout test.

webrtc/base/timeutils.cc

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 14 matching lines @@
 #include <mmsystem.h>
 #endif
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/timeutils.h"
 
 namespace rtc {
 
 ClockInterface* g_clock = nullptr;
 
-void SetClock(ClockInterface* clock) {
+ClockInterface* SetClockForTesting(ClockInterface* clock) {
+  ClockInterface* prev = g_clock;
   g_clock = clock;
+  return prev;
 }
 
 uint64_t TimeNanos() {
   if (g_clock) {
     return g_clock->TimeNanos();
   }
   int64_t ticks;
 #if defined(WEBRTC_MAC)
   static mach_timebase_info_data_t timebase;
   if (timebase.denom == 0) {
@@ skipping 122 matching lines @@
   if (expiry_in_leap_year && month <= 2 - 1) // |month| is zero based.
     day -= 1;
 
   // Combine all variables into seconds from 1970-01-01 00:00 (except |month|
   // which was accumulated into |day| above).
   return (((static_cast<int64_t>
             (year - 1970) * 365 + day) * 24 + hour) * 60 + min) * 60 + sec;
 }
 
 } // namespace rtc