Don't cache video codec list in VideoEngine2.

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 d1d162370d494c17649e21ec72b28f363d7143ac..8083c8edaccd6ea1ef2a9c8a2b3dfce1618b1695 100644
--- a/webrtc/media/base/mediaengine.h
+++ b/webrtc/media/base/mediaengine.h
@@ -74,7 +74,7 @@ class MediaEngineInterface {
   virtual const std::vector<AudioCodec>& audio_send_codecs() = 0;
   virtual const std::vector<AudioCodec>& audio_recv_codecs() = 0;
   virtual RtpCapabilities GetAudioCapabilities() = 0;
-  virtual const std::vector<VideoCodec>& video_codecs() = 0;
+  virtual std::vector<VideoCodec> video_codecs() = 0;
   virtual RtpCapabilities GetVideoCapabilities() = 0;
 
   // Starts AEC dump using existing file, a maximum file size in bytes can be
@@ -147,9 +147,7 @@ class CompositeMediaEngine : public MediaEngineInterface {
   virtual RtpCapabilities GetAudioCapabilities() {
     return voice_.GetCapabilities();
   }
-  virtual const std::vector<VideoCodec>& video_codecs() {
-    return video_.codecs();
-  }
+  virtual std::vector<VideoCodec> video_codecs() { return video_.codecs(); }
   virtual RtpCapabilities GetVideoCapabilities() {
     return video_.GetCapabilities();
   }