Add method Mutex::AssertHeld

Acts as a compile time annotation, with corresponding run-time check
only when DCHECKs are enabled, and built using absl or pthreads mutexes.

Bug: None
Change-Id: Ie044c1ea1e576df71d634301f7df9d75cdf10b1b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/226328
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34555}

modules/audio_processing/audio_processing_impl_unittest.cc

@@ -39,7 +39,8 @@ class MockInitialize : public AudioProcessingImpl {
       : AudioProcessingImpl(config) {}
 
   MOCK_METHOD(void, InitializeLocked, (), (override));
-  void RealInitializeLocked() RTC_NO_THREAD_SAFETY_ANALYSIS {
+  void RealInitializeLocked() {
+    AssertLockedForTest();
     AudioProcessingImpl::InitializeLocked();
   }