Fix compilation if HAVE_WEBRTC_VIDEO is not defined.

talk/media/webrtc/webrtcmediaengine.cc

 /*
  * libjingle
  * Copyright 2014 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 11 matching lines @@
  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "talk/media/webrtc/webrtcmediaengine.h"
 
 #include <algorithm>
 
+#ifdef HAVE_WEBRTC_VIDEO
 #include "talk/media/webrtc/webrtcvideoengine2.h"
+#else
+#include "talk/media/webrtc/nullwebrtcvideoengine.h"
+#endif
 #include "talk/media/webrtc/webrtcvoiceengine.h"
 
 namespace cricket {
 
 class WebRtcMediaEngine2
+#ifdef HAVE_WEBRTC_VIDEO
     : public CompositeMediaEngine<WebRtcVoiceEngine, WebRtcVideoEngine2> {
+#else
+    : public CompositeMediaEngine<WebRtcVoiceEngine, NullWebRtcVideoEngine> {
+#endif
  public:
   WebRtcMediaEngine2(webrtc::AudioDeviceModule* adm,
                      WebRtcVideoEncoderFactory* encoder_factory,
                      WebRtcVideoDecoderFactory* decoder_factory) {
     voice_.SetAudioDeviceModule(adm);
     video_.SetExternalDecoderFactory(decoder_factory);
     video_.SetExternalEncoderFactory(encoder_factory);
   }
 };
 
@@ skipping 97 matching lines @@
       kRtpTransportSequenceNumberHeaderExtension,
       kRtpAbsoluteSenderTimeHeaderExtension,
       kRtpTimestampOffsetHeaderExtension
     };
     DiscardRedundantExtensions(&result, kBweExtensionPriorities);
   }
 
   return result;
 }
 }  // namespace cricket