Move RefCountInterface to api/ and webrtc: namespace

This CL just moves the definition and adds a forward.
Actually using the new definition is left for later CLs.

Bug: webrtc:15622
Change-Id: I6d97ef45b98f9eb193c59dd7f8a89c99cfe0ba9a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/325381
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#41048}

api/BUILD.gn

@@ -438,6 +438,11 @@ rtc_source_set("wrapping_async_dns_resolver") {
   absl_deps = [ "//third_party/abseil-cpp/absl/memory" ]
 }
 
+rtc_source_set("ref_count") {
+  visibility = [ "*" ]
+  sources = [ "ref_count.h" ]
+}
+
 rtc_source_set("scoped_refptr") {
   visibility = [ "*" ]
   sources = [ "scoped_refptr.h" ]

api/ref_count.h

@@ -0,0 +1,67 @@
+/*
+ *  Copyright 2011 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 API_REF_COUNT_H_
+#define API_REF_COUNT_H_
+
+namespace webrtc {
+
+// Refcounted objects should implement the following informal interface:
+//
+// void AddRef() const ;
+// RefCountReleaseStatus Release() const;
+//
+// You may access members of a reference-counted object, including the AddRef()
+// and Release() methods, only if you already own a reference to it, or if
+// you're borrowing someone else's reference. (A newly created object is a
+// special case: the reference count is zero on construction, and the code that
+// creates the object should immediately call AddRef(), bringing the reference
+// count from zero to one, e.g., by constructing an rtc::scoped_refptr).
+//
+// AddRef() creates a new reference to the object.
+//
+// Release() releases a reference to the object; the caller now has one less
+// reference than before the call. Returns kDroppedLastRef if the number of
+// references dropped to zero because of this (in which case the object destroys
+// itself). Otherwise, returns kOtherRefsRemained, to signal that at the precise
+// time the caller's reference was dropped, other references still remained (but
+// if other threads own references, this may of course have changed by the time
+// Release() returns).
+//
+// The caller of Release() must treat it in the same way as a delete operation:
+// Regardless of the return value from Release(), the caller mustn't access the
+// object. The object might still be alive, due to references held by other
+// users of the object, but the object can go away at any time, e.g., as the
+// result of another thread calling Release().
+//
+// Calling AddRef() and Release() manually is discouraged. It's recommended to
+// use rtc::scoped_refptr to manage all pointers to reference counted objects.
+// Note that rtc::scoped_refptr depends on compile-time duck-typing; formally
+// implementing the below RefCountInterface is not required.
+
+enum class RefCountReleaseStatus { kDroppedLastRef, kOtherRefsRemained };
+
+// Interfaces where refcounting is part of the public api should
+// inherit this abstract interface. The implementation of these
+// methods is usually provided by the RefCountedObject template class,
+// applied as a leaf in the inheritance tree.
+class RefCountInterface {
+ public:
+  virtual void AddRef() const = 0;
+  virtual RefCountReleaseStatus Release() const = 0;
+
+  // Non-public destructor, because Release() has exclusive responsibility for
+  // destroying the object.
+ protected:
+  virtual ~RefCountInterface() {}
+};
+
+}  // namespace webrtc
+
+#endif  // API_REF_COUNT_H_

rtc_base/BUILD.gn

@@ -369,6 +369,7 @@ rtc_source_set("refcount") {
   ]
   deps = [
     ":macromagic",
+    "../api:ref_count",
     "../api:scoped_refptr",
   ]
 }

rtc_base/ref_count.h

@@ -10,57 +10,16 @@
 #ifndef RTC_BASE_REF_COUNT_H_
 #define RTC_BASE_REF_COUNT_H_
 
+// Transition file for backwards compatibility with source code
+// that includes the non-API file.
+
+#include "api/ref_count.h"
+
 namespace rtc {
 
-// Refcounted objects should implement the following informal interface:
-//
-// void AddRef() const ;
-// RefCountReleaseStatus Release() const;
-//
-// You may access members of a reference-counted object, including the AddRef()
-// and Release() methods, only if you already own a reference to it, or if
-// you're borrowing someone else's reference. (A newly created object is a
-// special case: the reference count is zero on construction, and the code that
-// creates the object should immediately call AddRef(), bringing the reference
-// count from zero to one, e.g., by constructing an rtc::scoped_refptr).
-//
-// AddRef() creates a new reference to the object.
-//
-// Release() releases a reference to the object; the caller now has one less
-// reference than before the call. Returns kDroppedLastRef if the number of
-// references dropped to zero because of this (in which case the object destroys
-// itself). Otherwise, returns kOtherRefsRemained, to signal that at the precise
-// time the caller's reference was dropped, other references still remained (but
-// if other threads own references, this may of course have changed by the time
-// Release() returns).
-//
-// The caller of Release() must treat it in the same way as a delete operation:
-// Regardless of the return value from Release(), the caller mustn't access the
-// object. The object might still be alive, due to references held by other
-// users of the object, but the object can go away at any time, e.g., as the
-// result of another thread calling Release().
-//
-// Calling AddRef() and Release() manually is discouraged. It's recommended to
-// use rtc::scoped_refptr to manage all pointers to reference counted objects.
-// Note that rtc::scoped_refptr depends on compile-time duck-typing; formally
-// implementing the below RefCountInterface is not required.
-
-enum class RefCountReleaseStatus { kDroppedLastRef, kOtherRefsRemained };
-
-// Interfaces where refcounting is part of the public api should
-// inherit this abstract interface. The implementation of these
-// methods is usually provided by the RefCountedObject template class,
-// applied as a leaf in the inheritance tree.
-class RefCountInterface {
- public:
-  virtual void AddRef() const = 0;
-  virtual RefCountReleaseStatus Release() const = 0;
-
-  // Non-public destructor, because Release() has exclusive responsibility for
-  // destroying the object.
- protected:
-  virtual ~RefCountInterface() {}
-};
+// TODO(bugs.webrtc.org/15622): Deprecate and remove these aliases.
+using webrtc::RefCountInterface;
+using webrtc::RefCountReleaseStatus;
 
 }  // namespace rtc