[Mojo Video Capture] Introduce abstraction BuildableVideoCaptureDevice

content/browser/renderer_host/media/ownership.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_BROWSER_RENDERER_HOST_MEDIA_OWNERSHIP_H_
+#define CONTENT_BROWSER_RENDERER_HOST_MEDIA_OWNERSHIP_H_
+
+#include <memory>
+#include <vector>
+
+#include "base/memory/ptr_util.h"
+#include "base/memory/ref_counted.h"
+
+namespace content {
+
+// Destructor-only interface for encapsulating pure ownership.
+// TODO(chfremer): Consider renaming this to Releasable, ScopedOpaqueReference,
+// ScopedReference, or ScopedResource.
+class Ownership {
+ public:
+  virtual ~Ownership() {}
+};
+
+// Encapsulates (shared) ownership of a scoped_refptr<T> and exposes it
+// through the Ownership interface.
+template <typename T>
+class ScopedRefptrOwnership : public Ownership {
+ public:
+  ScopedRefptrOwnership(scoped_refptr<T> refptr) : refptr_(std::move(refptr)) {}

[emircan, 2017/03/16 20:54:03]

Make this constructor to private and move MakeScopedRefptrOwnership here as a
static method?

[chfremer, 2017/03/16 22:02:30]

I moved the MakeScopedRefptrOwnership out of this class on purpose, because it
makes usage sites look a lot nicer by not requiring the template parameter to be
repeated.

MakeScopedRefptrOwnership(some_scoped_refptr_instance) 

vs. 

ScopedRefptrOwnership<SomeType>::CreateInstance(some_scoped_refptr_instance)

+
+ private:
+  const scoped_refptr<T> refptr_;
+};
+
+template <typename T>
+std::unique_ptr<Ownership> MakeScopedRefptrOwnership(scoped_refptr<T> refptr) {
+  return base::MakeUnique<ScopedRefptrOwnership<T>>(std::move(refptr));
+}
+
+// A collection of Ownerships
+class OwnershipCollection : public Ownership {
+ public:
+  OwnershipCollection();
+  ~OwnershipCollection() override;
+
+  void AttachOwnership(std::unique_ptr<Ownership> ownership) {
+    collection_.push_back(std::move(ownership));
+  }
+
+ private:
+  std::vector<std::unique_ptr<Ownership>> collection_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_OWNERSHIP_H_