Revert following changes for fixing Primetime issue:

- Issue #26 Part 2a: make more EME code conditional. (99118e38e)
- Issue #26 - Part 2b: Stub out GMPDecryptorProxy functions. (d44c61bf6)
- Issue #26 - Part 2c: Remove dependence on gmp/widevine-adapter/* (4c9689f68)
- Issue #1392 - Change --enable-eme to MOZ_ARG_ENABLE_BOOL and remove MOZ_EME_MODULES (832d84d2c)
- [Basilisk] Issue MoonchildProductions/UXP#1392 - Remove usage of MOZ_EME_MODULES (3a165cd)
- Issue #65 - Remove AppConstants from toolkit/mozapps/extensions (758618b60)

dom/media/MediaDecoderStateMachine.cpp

@@ -1238,12 +1238,7 @@ DecodeMetadataState::OnMetadataRead(MetadataHolder* aMetadata)
   // feeding in the CDM, which we need to decode the first frame (and
   // thus get the metadata). We could fix this if we could compute the start
   // time by demuxing without necessaring decoding.
-  bool waitingForCDM = 
-#ifdef MOZ_EME
-    mMaster->Info().IsEncrypted() && !mMaster->mCDMProxy;
-#else
-    false;
-#endif
+  bool waitingForCDM = Info().IsEncrypted() && !mMaster->mCDMProxy;
 
   mMaster->mNotifyMetadataBeforeFirstFrame =
     mMaster->mDuration.Ref().isSome() || waitingForCDM;
@@ -1267,9 +1262,7 @@ DormantState::HandlePlayStateChanged(MediaDecoder::PlayState aPlayState)
 {
   if (aPlayState == MediaDecoder::PLAY_STATE_PLAYING) {
     // Exit dormant when the user wants to play.
-#ifdef MOZ_EME
     MOZ_ASSERT(!Info().IsEncrypted() || mMaster->mCDMProxy);
-#endif
     MOZ_ASSERT(mMaster->mSentFirstFrameLoadedEvent);
     SetState<SeekingState>(Move(mPendingSeek), EventVisibility::Suppressed);
   }
@@ -1582,9 +1575,7 @@ ShutdownState::Enter()
   // dispose of the timer.
   master->mVideoDecodeSuspendTimer.Reset();
 
-#ifdef MOZ_EME
   master->mCDMProxyPromise.DisconnectIfExists();
-#endif
 
   if (master->IsPlaying()) {
     master->StopPlayback();
@@ -2138,12 +2129,10 @@ nsresult MediaDecoderStateMachine::Init(MediaDecoder* aDecoder)
 
   mMediaSink = CreateMediaSink(mAudioCaptured);
 
-#ifdef MOZ_EME
   mCDMProxyPromise.Begin(aDecoder->RequestCDMProxy()->Then(
     OwnerThread(), __func__, this,
     &MediaDecoderStateMachine::OnCDMProxyReady,
     &MediaDecoderStateMachine::OnCDMProxyNotReady));
-#endif
 
   nsresult rv = mReader->Init();
   NS_ENSURE_SUCCESS(rv, rv);
@@ -3119,7 +3108,6 @@ void MediaDecoderStateMachine::OnMediaSinkAudioError(nsresult aResult)
   DecodeError(MediaResult(NS_ERROR_DOM_MEDIA_MEDIASINK_ERR, __func__));
 }
 
-#ifdef MOZ_EME
 void
 MediaDecoderStateMachine::OnCDMProxyReady(RefPtr<CDMProxy> aProxy)
 {
@@ -3136,7 +3124,6 @@ MediaDecoderStateMachine::OnCDMProxyNotReady()
   MOZ_ASSERT(OnTaskQueue());
   mCDMProxyPromise.Complete();
 }
-#endif
 
 void
 MediaDecoderStateMachine::SetAudioCaptured(bool aCaptured)