Issue #80 - De-unify dom/media part 3

Excluding /dom/media/webrtc for bad template use:
MediaTrackConstraints.cpp/h
MediaEngineCameraVideoSource.cpp and
MediaEngineRemoteVideoSource.cpp

dom/media/webrtc/moz.build

@@ -31,15 +31,14 @@ if CONFIG['MOZ_WEBRTC']:
     UNIFIED_SOURCES += [
         'MediaEngineCameraVideoSource.cpp',
         'MediaEngineRemoteVideoSource.cpp',
+    ]
+    SOURCES += [
         'MediaEngineTabVideoSource.cpp',
+        'MediaEngineWebRTC.cpp',
         'MediaEngineWebRTCAudio.cpp',
         'RTCCertificate.cpp',
         'RTCIdentityProviderRegistrar.cpp',
     ]
-    # MediaEngineWebRTC.cpp needs to be built separately.
-    SOURCES += [
-        'MediaEngineWebRTC.cpp',
-    ]
     LOCAL_INCLUDES += [
         '/dom/base',
         '/media/libyuv/include',
@@ -53,8 +52,10 @@ XPIDL_SOURCES += [
 ]
 
 UNIFIED_SOURCES += [
-    'MediaEngineDefault.cpp',
     'MediaTrackConstraints.cpp',
+]
+SOURCES += [
+    'MediaEngineDefault.cpp',
     'PeerIdentity.cpp',
 ]