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}

rtc_base/system/thread_registry.h

@@ -0,0 +1,46 @@
+/*
+ *  Copyright 2019 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_SYSTEM_THREAD_REGISTRY_H_
+#define RTC_BASE_SYSTEM_THREAD_REGISTRY_H_
+
+#include "rtc_base/location.h"
+
+namespace webrtc {
+
+class ScopedRegisterThreadForDebugging {
+ public:
+#if defined(WEBRTC_ANDROID) && !defined(WEBRTC_CHROMIUM_BUILD)
+  explicit ScopedRegisterThreadForDebugging(rtc::Location location);
+  ~ScopedRegisterThreadForDebugging();
+#else
+  explicit ScopedRegisterThreadForDebugging(rtc::Location) {}
+#endif
+
+  // Not movable or copyable, because we can't duplicate the resource it owns,
+  // and it needs a constant address.
+  ScopedRegisterThreadForDebugging(const ScopedRegisterThreadForDebugging&) =
+      delete;
+  ScopedRegisterThreadForDebugging(ScopedRegisterThreadForDebugging&&) = delete;
+  ScopedRegisterThreadForDebugging& operator=(
+      const ScopedRegisterThreadForDebugging&) = delete;
+  ScopedRegisterThreadForDebugging& operator=(
+      ScopedRegisterThreadForDebugging&&) = delete;
+};
+
+#if defined(WEBRTC_ANDROID) && !defined(WEBRTC_CHROMIUM_BUILD)
+void PrintStackTracesOfRegisteredThreads();
+#else
+inline void PrintStackTracesOfRegisteredThreads() {}
+#endif
+
+}  // namespace webrtc
+
+#endif  // RTC_BASE_SYSTEM_THREAD_REGISTRY_H_