Let threads opt in to having their stack traces printed

The video decoder thread is the pilot user.

For now this is an Android-only feature, since that's the only
platform we can print stack traces on.

Bug: webrtc:9987
Change-Id: Ie638c619673b5f159d91a32683fd787baf46479a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/126222
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27127}

sdk/android/src/jni/pc/peer_connection_factory.cc

@@ -23,6 +23,7 @@
 // The user may pass in a nullptr.
 #include "modules/audio_processing/include/audio_processing.h"  // nogncheck
 #include "rtc_base/event_tracer.h"
+#include "rtc_base/system/thread_registry.h"
 #include "rtc_base/thread.h"
 #include "sdk/android/generated_peerconnection_jni/jni/PeerConnectionFactory_jni.h"
 #include "sdk/android/native_api/jni/java_types.h"
@@ -520,5 +521,10 @@ static void JNI_PeerConnectionFactory_PrintStackTrace(JNIEnv* env, jint tid) {
   RTC_LOG(LS_WARNING) << StackTraceToString(GetStackTrace(tid));
 }
 
+static void JNI_PeerConnectionFactory_PrintStackTracesOfRegisteredThreads(
+    JNIEnv* env) {
+  PrintStackTracesOfRegisteredThreads();
+}
+
 }  // namespace jni
 }  // namespace webrtc