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/moz.build

@@ -35,6 +35,8 @@ EXPORTS += [
     'GMPAudioDecoderProxy.h',
     'GMPAudioHost.h',
     'GMPCallbackBase.h',
+    'GMPCDMCallbackProxy.h',
+    'GMPCDMProxy.h',
     'GMPChild.h',
     'GMPContentChild.h',
     'GMPContentParent.h',
@@ -71,12 +73,6 @@ EXPORTS += [
     'GMPVideoPlaneImpl.h',
 ]
 
-if CONFIG['MOZ_EME']:
-    EXPORTS += [
-        'GMPCDMCallbackProxy.h',
-        'GMPCDMProxy.h',
-    ]
-
 # We link GMPLoader into xul on B2G/Fennec as its code does not need to be
 # covered by a DRM vendor's voucher.
 if CONFIG['OS_TARGET'] == 'Android':
@@ -91,6 +87,8 @@ UNIFIED_SOURCES += [
     'GMPAudioDecoderChild.cpp',
     'GMPAudioDecoderParent.cpp',
     'GMPAudioHost.cpp',
+    'GMPCDMCallbackProxy.cpp',
+    'GMPCDMProxy.cpp',
     'GMPChild.cpp',
     'GMPContentChild.cpp',
     'GMPContentParent.cpp',
@@ -122,16 +120,10 @@ UNIFIED_SOURCES += [
     'GMPVideoPlaneImpl.cpp',
 ]
 
-if CONFIG['MOZ_EME']:
-    UNIFIED_SOURCES += [
-        'GMPCDMCallbackProxy.cpp',
-        'GMPCDMProxy.cpp',
-    ]
-
-DIRS += ['rlz']
-
-if CONFIG['MOZ_EME']:
-    DIRS += ['widevine-adapter']
+DIRS += [
+    'rlz',
+    'widevine-adapter',
+]
 
 IPDL_SOURCES += [
   'GMPTypes.ipdlh',