[Chromecast] Nullable MediaResourceTracker in CastCdm

This means the implementation doesn't need hardware resource.

Bug: internal b/141143745
Test: Widevine content
Merge-With: eureka-internal/327150
Change-Id: Ia6d5494b19301311b6d70836c0ef4d9f36bbba6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1869931Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Commit-Queue: Yuchen Liu <yucliu@chromium.org>
Auto-Submit: Yuchen Liu <yucliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708361}

chromecast/media/cdm/cast_cdm.cc

@@ -104,7 +104,6 @@ int HdcpVersionX10(::media::HdcpVersion hdcp_version) {
 CastCdm::CastCdm(MediaResourceTracker* media_resource_tracker)
     : media_resource_tracker_(media_resource_tracker),
       cast_cdm_context_(new CastCdmContextImpl(this)) {
-  DCHECK(media_resource_tracker);
   thread_checker_.DetachFromThread();
 }
 
@@ -112,7 +111,6 @@ CastCdm::~CastCdm() {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(player_tracker_impl_.get());
   player_tracker_impl_->NotifyCdmUnset();
-  media_resource_tracker_->DecrementUsageCount();
 }
 
 void CastCdm::Initialize(
@@ -122,7 +120,11 @@ void CastCdm::Initialize(
     const ::media::SessionExpirationUpdateCB& session_expiration_update_cb) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  media_resource_tracker_->IncrementUsageCount();
+  if (media_resource_tracker_) {
+    media_resource_usage_ = std::make_unique<MediaResourceTracker::ScopedUsage>(
+        media_resource_tracker_);
+  }
+
   player_tracker_impl_.reset(new ::media::PlayerTrackerImpl());
 
   session_message_cb_ = session_message_cb;

chromecast/media/cdm/cast_cdm.h

@@ -103,7 +103,10 @@ class CastCdm : public ::media::ContentDecryptionModule {
   ::media::SessionKeysChangeCB session_keys_change_cb_;
   ::media::SessionExpirationUpdateCB session_expiration_update_cb_;
 
-  MediaResourceTracker* media_resource_tracker_;
+  // Track the usage for hardware resource. nullptr means the implementation
+  // doesn't need hardware resource.
+  MediaResourceTracker* const media_resource_tracker_;
+  std::unique_ptr<MediaResourceTracker::ScopedUsage> media_resource_usage_;
   std::unique_ptr<::media::PlayerTrackerImpl> player_tracker_impl_;
   std::unique_ptr<CastCdmContext> cast_cdm_context_;