Reland "Migrate test/time_controller to webrtc::Mutex."

This is a reland of 52fd96fb731d9a911bd064a9718d96fef0bd5b24

Original change's description:
> Migrate test/time_controller to webrtc::Mutex.
>
> Bug: webrtc:11567
> Change-Id: I26fb07bf84ed197ce667290aa0bf4816bc9c5c06
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/178818
> Reviewed-by: Sebastian Jansson <srte@webrtc.org>
> Commit-Queue: Markus Handell <handellm@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#31660}

Bug: webrtc:11567
Change-Id: I4979b6be8ac5ec661e0f18cca4d0c185916233bb
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/178876
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Commit-Queue: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31687}

test/time_controller/simulated_thread.cc

diff --git a/test/time_controller/simulated_thread.cc b/test/time_controller/simulated_thread.cc
index 8d1637c..8071264 100644
--- a/test/time_controller/simulated_thread.cc
+++ b/test/time_controller/simulated_thread.cc
@@ -59,7 +59,7 @@
   CurrentThreadSetter set_current(this);
   ProcessMessages(0);
   int delay_ms = GetDelay();
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   if (delay_ms == kForever) {
     next_run_time_ = Timestamp::PlusInfinity();
   } else {
@@ -95,7 +95,7 @@
                            rtc::MessageData* pdata,
                            bool time_sensitive) {
   rtc::Thread::Post(posted_from, phandler, id, pdata, time_sensitive);
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   next_run_time_ = Timestamp::MinusInfinity();
 }
 
@@ -105,7 +105,7 @@
                                   uint32_t id,
                                   rtc::MessageData* pdata) {
   rtc::Thread::PostDelayed(posted_from, delay_ms, phandler, id, pdata);
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   next_run_time_ =
       std::min(next_run_time_, Timestamp::Millis(rtc::TimeMillis() + delay_ms));
 }
@@ -116,7 +116,7 @@
                              uint32_t id,
                              rtc::MessageData* pdata) {
   rtc::Thread::PostAt(posted_from, target_time_ms, phandler, id, pdata);
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   next_run_time_ = std::min(next_run_time_, Timestamp::Millis(target_time_ms));
 }