--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -2695,23 +2695,23 @@ MediaDecoderStateMachine::SizeOfVideoQue
 
 size_t
 MediaDecoderStateMachine::SizeOfAudioQueue() const
 {
   return mReader->SizeOfAudioQueueInBytes();
 }
 
 AbstractCanonical<media::TimeIntervals>*
-MediaDecoderStateMachine::CanonicalBuffered()
+MediaDecoderStateMachine::CanonicalBuffered() const
 {
   return mReader->CanonicalBuffered();
 }
 
 MediaEventSource<void>&
-MediaDecoderStateMachine::OnMediaNotSeekable()
+MediaDecoderStateMachine::OnMediaNotSeekable() const
 {
   return mReader->OnMediaNotSeekable();
 }
 
 } // namespace mozilla
 
 // avoid redefined macro in unified build
 #undef LOG

--- a/dom/media/MediaDecoderStateMachine.h
+++ b/dom/media/MediaDecoderStateMachine.h
@@ -217,17 +217,17 @@ public:
     MOZ_ASSERT(NS_IsMainThread());
     mResource = nullptr;
   }
 
   TimedMetadataEventSource& TimedMetadataEvent() {
     return mMetadataManager.TimedMetadataEvent();
   }
 
-  MediaEventSource<void>& OnMediaNotSeekable();
+  MediaEventSource<void>& OnMediaNotSeekable() const;
 
   MediaEventSourceExc<nsAutoPtr<MediaInfo>,
                       nsAutoPtr<MetadataTags>,
                       MediaDecoderEventVisibility>&
   MetadataLoadedEvent() { return mMetadataLoadedEvent; }
 
   MediaEventSourceExc<nsAutoPtr<MediaInfo>,
                       MediaDecoderEventVisibility>&
@@ -1034,17 +1034,17 @@ private:
 
   // Current playback position in the stream in bytes.
   Canonical<int64_t> mPlaybackOffset;
 
   // Used to distiguish whether the audio is producing sound.
   Canonical<bool> mIsAudioDataAudible;
 
 public:
-  AbstractCanonical<media::TimeIntervals>* CanonicalBuffered();
+  AbstractCanonical<media::TimeIntervals>* CanonicalBuffered() const;
 
   AbstractCanonical<media::NullableTimeUnit>* CanonicalDuration() {
     return &mDuration;
   }
   AbstractCanonical<bool>* CanonicalIsShutdown() {
     return &mIsShutdown;
   }
   AbstractCanonical<NextFrameStatus>* CanonicalNextFrameStatus() {