Revert "Refactor the PlatformThread API."

This reverts commit c89fdd716c4c8af608017c76f75bf27e4c3d602e.

Reason for revert: Causes rare compilation error on win-libfuzzer-asan trybot.
See https://ci.chromium.org/p/chromium/builders/try/win-libfuzzer-asan-rel/713745?

Original change's description:
> Refactor the PlatformThread API.
>
> PlatformThread's API is using old style function pointers, causes
> casting, is unintuitive and forces artificial call sequences, and
> is additionally possible to misuse in release mode.
>
> Fix this by an API face lift:
> 1. The class is turned into a handle, which can be empty.
> 2. The only way of getting a non-empty PlatformThread is by calling
> SpawnJoinable or SpawnDetached, clearly conveying the semantics to the
> code reader.
> 3. Handles can be Finalized, which works differently for joinable and
> detached threads:
>   a) Handles for detached threads are simply closed where applicable.
>   b) Joinable threads are joined before handles are closed.
> 4. The destructor finalizes handles. No explicit call is needed.
>
> Fixed: webrtc:12727
> Change-Id: Id00a0464edf4fc9e552b6a1fbb5d2e1280e88811
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215075
> Commit-Queue: Markus Handell <handellm@webrtc.org>
> Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Reviewed-by: Tommi <tommi@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#33923}

# Not skipping CQ checks because original CL landed > 1 day ago.

TBR=handellm@webrtc.org

Bug: webrtc:12727
Change-Id: Ic0146be8866f6dd3ad9c364fb8646650b8e07419
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/217583
Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
Reviewed-by: Markus Handell <handellm@webrtc.org>
Commit-Queue: Guido Urdaneta <guidou@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33936}
diff --git a/rtc_base/logging_unittest.cc b/rtc_base/logging_unittest.cc
index dc1208f..225d66d 100644
--- a/rtc_base/logging_unittest.cc
+++ b/rtc_base/logging_unittest.cc
@@ -160,13 +160,18 @@
 
 class LogThread {
  public:
-  void Start() {
-    thread_ = PlatformThread::SpawnJoinable(
-        [] { RTC_LOG(LS_VERBOSE) << "RTC_LOG"; }, "LogThread");
-  }
+  LogThread() : thread_(&ThreadEntry, this, "LogThread") {}
+  ~LogThread() { thread_.Stop(); }
+
+  void Start() { thread_.Start(); }
 
  private:
+  void Run() { RTC_LOG(LS_VERBOSE) << "RTC_LOG"; }
+
+  static void ThreadEntry(void* p) { static_cast<LogThread*>(p)->Run(); }
+
   PlatformThread thread_;
+  Event event_;
 };
 
 // Ensure we don't crash when adding/removing streams while threads are going.