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/gmp/GMPParent.cpp

@@ -30,10 +30,8 @@ using mozilla::ipc::GeckoChildProcessHost;
 #include "WMFDecoderModule.h"
 #endif
 
-#ifdef MOZ_EME
 #include "mozilla/dom/WidevineCDMManifestBinding.h"
 #include "widevine-adapter/WidevineAdapter.h"
-#endif
 
 namespace mozilla {
 
@@ -656,7 +654,6 @@ GMPParent::ReadGMPMetaData()
     return ReadGMPInfoFile(infoFile);
   }
 
-#ifdef MOZ_EME
   // Maybe this is the Widevine adapted plugin?
   nsCOMPtr<nsIFile> manifestFile;
   rv = mDirectory->Clone(getter_AddRefs(manifestFile));
@@ -665,9 +662,6 @@ GMPParent::ReadGMPMetaData()
   }
   manifestFile->AppendRelativePath(NS_LITERAL_STRING("manifest.json"));
   return ReadChromiumManifestFile(manifestFile);
-#else
-  return GenericPromise::CreateAndReject(NS_ERROR_FAILURE, __func__);
-#endif
 }
 
 RefPtr<GenericPromise>
@@ -770,7 +764,6 @@ GMPParent::ReadChromiumManifestFile(nsIFile* aFile)
 RefPtr<GenericPromise>
 GMPParent::ParseChromiumManifest(nsString aJSON)
 {
-#ifdef MOZ_EME
   LOGD("%s: for '%s'", __FUNCTION__, NS_LossyConvertUTF16toASCII(aJSON).get());
 
   MOZ_ASSERT(NS_IsMainThread());
@@ -808,10 +801,6 @@ GMPParent::ParseChromiumManifest(nsString aJSON)
 #endif
 
   return GenericPromise::CreateAndResolve(true, __func__);
-#else  // !MOZ_EME
-  MOZ_ASSERT_UNREACHABLE("don't call me if EME isn't enabled");
-  return GenericPromise::CreateAndReject(NS_ERROR_FAILURE, __func__);
-#endif // !MOZ_EME
 }
 
 bool