Revert of Clean up unused cricket::VideoCapturer inclusion from mediaengine.h

webrtc/media/base/mediaengine.h

Index: webrtc/media/base/mediaengine.h
diff --git a/webrtc/media/base/mediaengine.h b/webrtc/media/base/mediaengine.h
index 4fbb71b17cd035d6c227e133b1616484265e8f43..dd1f5272a067dc21599eef469e71364ef9035ac7 100644
--- a/webrtc/media/base/mediaengine.h
+++ b/webrtc/media/base/mediaengine.h
@@ -25,6 +25,7 @@
 #include "webrtc/media/base/codec.h"
 #include "webrtc/media/base/mediachannel.h"
 #include "webrtc/media/base/mediacommon.h"
+#include "webrtc/media/base/videocapturer.h"
 #include "webrtc/media/base/videocommon.h"
 #include "webrtc/modules/audio_coding/codecs/audio_decoder_factory.h"
 
@@ -38,6 +39,8 @@
 }
 
 namespace cricket {
+
+class VideoCapturer;
 
 struct RtpCapabilities {
   std::vector<webrtc::RtpExtension> header_extensions;