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/MediaDecoder.cpp

@@ -387,9 +387,7 @@ MediaDecoder::MediaDecoder(MediaDecoderOwner* aOwner)
   , mLogicalPosition(0.0)
   , mDuration(std::numeric_limits<double>::quiet_NaN())
   , mResourceCallback(new ResourceCallback())
-#ifdef MOZ_EME
   , mCDMProxyPromise(mCDMProxyPromiseHolder.Ensure(__func__))
-#endif
   , mIgnoreProgressData(false)
   , mInfiniteStream(false)
   , mOwner(aOwner)
@@ -474,9 +472,7 @@ MediaDecoder::Shutdown()
 
   mResourceCallback->Disconnect();
 
-#ifdef MOZ_EME
   mCDMProxyPromiseHolder.RejectIfExists(true, __func__);
-#endif
 
   DiscardOngoingSeekIfExists();
 
@@ -1541,7 +1537,6 @@ MediaDecoder::CanPlayThrough()
   return GetStatistics().CanPlayThrough();
 }
 
-#ifdef MOZ_EME
 RefPtr<MediaDecoder::CDMProxyPromise>
 MediaDecoder::RequestCDMProxy() const
 {
@@ -1556,7 +1551,6 @@ MediaDecoder::SetCDMProxy(CDMProxy* aProxy)
 
   mCDMProxyPromiseHolder.ResolveIfExists(aProxy, __func__);
 }
-#endif
 
 bool
 MediaDecoder::IsOpusEnabled()