Don't cache video codec list in VideoEngine2.

webrtc/media/engine/webrtcvideoengine2.h

Index: webrtc/media/engine/webrtcvideoengine2.h
diff --git a/webrtc/media/engine/webrtcvideoengine2.h b/webrtc/media/engine/webrtcvideoengine2.h
index 20884e8bee1a65cbd1a7d2c9b2df913bc4601414..aa116ed31897c73ded1c9caf81a39d2eece94913 100644
--- a/webrtc/media/engine/webrtcvideoengine2.h
+++ b/webrtc/media/engine/webrtcvideoengine2.h
@@ -102,7 +102,7 @@ class WebRtcVideoEngine2 {
                                      const MediaConfig& config,
                                      const VideoOptions& options);
 
-  const std::vector<VideoCodec>& codecs() const;
+  std::vector<VideoCodec> codecs() const;
   RtpCapabilities GetCapabilities() const;
 
   // Set a WebRtcVideoDecoderFactory for external decoding. Video engine does
@@ -116,8 +116,6 @@ class WebRtcVideoEngine2 {
       WebRtcVideoEncoderFactory* encoder_factory);
 
  private:
-  std::vector<VideoCodec> video_codecs_;
-
   bool initialized_;
 
   WebRtcVideoDecoderFactory* external_decoder_factory_;