Revert of Improving the fake clock and using it to fix a flaky STUN timeout test. (patchset #10 id:180001 of https://codereview.webrtc.org/2024813004/ )

Reason for revert:
There seems to be a TSan warning that wasn't caught by the trybot: https://build.chromium.org/p/client.webrtc/builders/Linux%20Tsan%20v2/builds/6732/steps/peerconnection_unittests/logs/stdio

Apparently a thread is still alive even after destroying WebRTCSession. Need to think of a way to fix this, without adding a critical section around g_clock (since that would hurt performance).

Original issue's description:
> Improving the fake clock and using it to fix a flaky STUN timeout test.
>
> When the fake clock's time is advanced, it now ensures all pending
> queued messages have been dispatched. This allows us to write a
> "SIMULATED_WAIT" macro that ticks the simulated clock by milliseconds up
> until the target time.
>
> Useful in this case, where we know the STUN timeout should take a total
> of 9500ms, but it would be overly complex to write test code that waits
> for each individual timeout, ensures a STUN packet has been
> retransmited, etc.
>
> (The test described above *should* be written, but it belongs in
> p2ptransportchannel_unittest.cc, not webrtcsession_unittest.cc).
>
> Committed: https://crrev.com/ffbe0e17e2c9b7fe101023acf40574dc0c95631a
> Cr-Commit-Position: refs/heads/master@{#13043}

TBR=pthatcher@webrtc.org,tommi@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review-Url: https://codereview.webrtc.org/2038213002
Cr-Commit-Position: refs/heads/master@{#13045}

webrtc/base/timeutils_unittest.cc

@@ -301,7 +301,7 @@ TEST(TimeDelta, NumericOperators) {
 // fake clock when it's set.
 TEST(FakeClock, TimeFunctionsUseFakeClock) {
   FakeClock clock;
-  SetClockForTesting(&clock);
+  SetClock(&clock);
 
   clock.SetTimeNanos(987654321u);
   EXPECT_EQ(987u, Time32());
@@ -310,7 +310,7 @@ TEST(FakeClock, TimeFunctionsUseFakeClock) {
   EXPECT_EQ(987654321u, TimeNanos());
   EXPECT_EQ(1000u, TimeAfter(13));
 
-  SetClockForTesting(nullptr);
+  SetClock(nullptr);
   // After it's unset, we should get a normal time.
   EXPECT_NE(987, TimeMillis());
 }
@@ -348,7 +348,7 @@ TEST(FakeClock, SettingTimeWakesThreads) {
   int64_t real_start_time_ms = TimeMillis();
 
   FakeClock clock;
-  SetClockForTesting(&clock);
+  SetClock(&clock);
 
   Thread worker;
   worker.Start();
@@ -359,25 +359,24 @@ TEST(FakeClock, SettingTimeWakesThreads) {
     message_handler_dispatched.Set();
   };
   FunctorMessageHandler<void, decltype(functor)> handler(functor);
-  worker.PostDelayed(60000, &handler);
+  worker.PostDelayed(10000, &handler);
 
   // Wait for a bit for the worker thread to be started and enter its socket
-  // select(). Otherwise this test would be trivial since the worker thread
-  // would process the event as soon as it was started.
+  // select().
   Thread::Current()->SleepMs(1000);
 
   // Advance the fake clock, expecting the worker thread to wake up
-  // and dispatch the message instantly.
-  clock.AdvanceTime(TimeDelta::FromSeconds(60u));
-  EXPECT_TRUE(message_handler_dispatched.Wait(0));
+  // and dispatch the message quickly.
+  clock.AdvanceTime(TimeDelta::FromSeconds(10u));
+  message_handler_dispatched.Wait(Event::kForever);
   worker.Stop();
 
-  SetClockForTesting(nullptr);
+  SetClock(nullptr);
 
-  // The message should have been dispatched long before the 60 seconds fully
-  // elapsed (just a sanity check).
+  // The message should have been dispatched long before the 10 seconds fully
+  // elapsed.
   int64_t real_end_time_ms = TimeMillis();
-  EXPECT_LT(real_end_time_ms - real_start_time_ms, 10000);
+  EXPECT_LT(real_end_time_ms - real_start_time_ms, 2000);
 }
 
 }  // namespace rtc