[chromecast] Track MediaPipelineBackend used by CastRenderer.

chromecast/media/base/media_resource_tracker.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 CHROMECAST_MEDIA_BASE_MEDIA_RESOURCE_TRACKER_H_
 #define CHROMECAST_MEDIA_BASE_MEDIA_RESOURCE_TRACKER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/sequenced_task_runner_helpers.h"
@@ skipping 14 matching lines @@
 // CastMediaShlib::Initialize/Finalize through this interface.
 // Threading model and lifetime:
 // * This class interacts on both UI and media threads (task runners required
 //   by ctor to perform thread hopping and checks). See function-level comments
 //   on which thread to use for which operations.
 // * The application should instantiate a single MediaResourceTracker instance.
 //   Destruction should be performed by calling FinalizeAndDestroy from the UI
 //   thread.
 class MediaResourceTracker {
  public:
+  // Helper class to manage media resource usage count.
+  // Create an instance of this class when a media resource is created.
+  // Delete the instance *after* the media resource is deleted.
+  // This class is not thread-safe. It must be created and deleted on
+  // |MediaResourceTracker::media_task_runner_|.
+  class ScopedUsage {
+   public:
+    ScopedUsage(MediaResourceTracker* tracker);
+    ~ScopedUsage();
+
+   private:
+    MediaResourceTracker* tracker_;
+    DISALLOW_COPY_AND_ASSIGN(ScopedUsage);
+  };
+
   MediaResourceTracker(
       const scoped_refptr<base::SingleThreadTaskRunner>& ui_task_runner,
       const scoped_refptr<base::SingleThreadTaskRunner>& media_task_runner);
 
   // Media resource acquire implementation. Must call on ui thread; runs
   // CastMediaShlib::Initialize on media thread.  Safe to call even if media lib
   // already initialized.
   void InitializeMediaLib();
 
   // Media resource release implementation:
@@ skipping 41 matching lines @@
   scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner_;
   scoped_refptr<base::SingleThreadTaskRunner> media_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaResourceTracker);
 };
 
 }  // namespace media
 }  // namespace chromecast
 
 #endif  // CHROMECAST_MEDIA_BASE_MEDIA_RESOURCE_TRACKER_H_