[chromecast] Track MediaPipelineBackend used by CastRenderer.

chromecast/media/base/media_resource_tracker.cc

Index: chromecast/media/base/media_resource_tracker.cc
diff --git a/chromecast/media/base/media_resource_tracker.cc b/chromecast/media/base/media_resource_tracker.cc
index 79b4c12f5d04577cc314e3dbaa3a64bd39e298f0..0052f58cfebe3446925337d13cebd0a90d32aec9 100644
--- a/chromecast/media/base/media_resource_tracker.cc
+++ b/chromecast/media/base/media_resource_tracker.cc
@@ -12,6 +12,18 @@
 namespace chromecast {
 namespace media {
 
+MediaResourceTracker::ScopedUsage::ScopedUsage(MediaResourceTracker* tracker)
+    : tracker_(tracker) {
+  DCHECK(tracker_);
+  DCHECK(tracker_->media_task_runner_->BelongsToCurrentThread());
+  tracker_->IncrementUsageCount();
+}
+
+MediaResourceTracker::ScopedUsage::~ScopedUsage() {
+  DCHECK(tracker_->media_task_runner_->BelongsToCurrentThread());
+  tracker_->DecrementUsageCount();
+}
+
 MediaResourceTracker::MediaResourceTracker(
     const scoped_refptr<base::SingleThreadTaskRunner>& ui_task_runner,
     const scoped_refptr<base::SingleThreadTaskRunner>& media_task_runner)