Fix compilation if HAVE_WEBRTC_VIDEO is not defined.

talk/media/webrtc/webrtcvideocapturerfactory.cc

Index: talk/media/webrtc/webrtcvideocapturerfactory.cc
diff --git a/talk/media/webrtc/webrtcvideocapturerfactory.cc b/talk/media/webrtc/webrtcvideocapturerfactory.cc
index 9f542bd9c1b15c0e7d767360230f6f9895bd0223..e1466fbba46ffbb54c4ca1d91ff0abfd75c9421c 100755
--- a/talk/media/webrtc/webrtcvideocapturerfactory.cc
+++ b/talk/media/webrtc/webrtcvideocapturerfactory.cc
@@ -32,12 +32,16 @@
 namespace cricket {
 
 VideoCapturer* WebRtcVideoDeviceCapturerFactory::Create(const Device& device) {
+#ifdef HAVE_WEBRTC_VIDEO
   rtc::scoped_ptr<WebRtcVideoCapturer> capturer(
       new WebRtcVideoCapturer());
   if (!capturer->Init(device)) {
-    return NULL;
+    return nullptr;
   }
   return capturer.release();
+#else
+  return nullptr;
+#endif
 }
 
 }  // namespace cricket