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}
diff --git a/sdk/android/native_unittests/stacktrace/stacktrace_unittest.cc b/sdk/android/native_unittests/stacktrace/stacktrace_unittest.cc
index fcd9c9b..b77d867 100644
--- a/sdk/android/native_unittests/stacktrace/stacktrace_unittest.cc
+++ b/sdk/android/native_unittests/stacktrace/stacktrace_unittest.cc
@@ -153,28 +153,24 @@
   }
 };
 
-// This is the function that is exectued by the thread that will deadlock and
-// have its stacktrace captured.
-void ThreadFunction(void* void_params) {
-  ThreadParams* params = static_cast<ThreadParams*>(void_params);
-  params->tid = gettid();
-
-  params->deadlock_region_start_address = GetCurrentRelativeExecutionAddress();
-  params->deadlock_start_event.Set();
-  params->deadlock_impl->Deadlock();
-  params->deadlock_region_end_address = GetCurrentRelativeExecutionAddress();
-
-  params->deadlock_done_event.Set();
-}
-
 void TestStacktrace(std::unique_ptr<DeadlockInterface> deadlock_impl) {
   // Set params that will be sent to other thread.
   ThreadParams params;
   params.deadlock_impl = deadlock_impl.get();
 
   // Spawn thread.
-  rtc::PlatformThread thread(&ThreadFunction, &params, "StacktraceTest");
-  thread.Start();
+  auto thread = rtc::PlatformThread::SpawnJoinable(
+      [&params] {
+        params.tid = gettid();
+        params.deadlock_region_start_address =
+            GetCurrentRelativeExecutionAddress();
+        params.deadlock_start_event.Set();
+        params.deadlock_impl->Deadlock();
+        params.deadlock_region_end_address =
+            GetCurrentRelativeExecutionAddress();
+        params.deadlock_done_event.Set();
+      },
+      "StacktraceTest");
 
   // Wait until the thread has entered the deadlock region, and take a very
   // brief nap to give it time to reach the actual deadlock.
@@ -198,8 +194,6 @@
       << rtc::ToHex(params.deadlock_region_start_address) << ", "
       << rtc::ToHex(params.deadlock_region_end_address)
       << "] not contained in: " << StackTraceToString(stack_trace);
-
-  thread.Stop();
 }
 
 class LookoutLogSink final : public rtc::LogSink {
@@ -259,13 +253,9 @@
 
   // Start a thread that waits for an event.
   rtc::Event ev;
-  rtc::PlatformThread thread(
-      [](void* arg) {
-        auto* ev = static_cast<rtc::Event*>(arg);
-        ev->Wait(rtc::Event::kForever);
-      },
-      &ev, "TestRtcEventDeadlockDetection");
-  thread.Start();
+  auto thread = rtc::PlatformThread::SpawnJoinable(
+      [&ev] { ev.Wait(rtc::Event::kForever); },
+      "TestRtcEventDeadlockDetection");
 
   // The message should appear after 3 sec. We'll wait up to 10 sec in an
   // attempt to not be flaky.
@@ -273,7 +263,7 @@
 
   // Unblock the thread and shut it down.
   ev.Set();
-  thread.Stop();
+  thread.Finalize();
   rtc::LogMessage::RemoveLogToStream(&sink);
 }