Revert of Stop caching supported codecs in WebRtcVideoEngine2 (patchset #1 id:1 of https://codereview.webrtc.org/2492473002/ )

Reason for revert:
This CL probably broke Chromium FYI.

Original issue's description:
> Stop caching supported codecs in WebRtcVideoEngine2
>
> We currently cache the result of GetSupportedCodecs in a member variable
> |video_codecs_| in WebRtcVideoEngine2. This means we need to keep
> |video_codecs_| and the result of GetSupportedCodecs in sync, which is
> error prone. It's simpler to just call GetSupportedCodecs when we need
> it, and we actually end up making fewer calls, so it's faster as well.
> This CL also returns all std::vectors by-value instead of by-ref. Move
> semantic together with in-place filtering of codecs actually end up with
> fewer copies, and it's also simpler to not return references.
>
> BUG=webrtc:6337
>
> Committed: https://crrev.com/9f71ec5a3e3175751f4475b126cfda89767363f2
> Cr-Commit-Position: refs/heads/master@{#15007}

TBR=tommi@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:6337

Review-Url: https://codereview.webrtc.org/2489173004
Cr-Commit-Position: refs/heads/master@{#15014}
diff --git a/webrtc/pc/channelmanager.h b/webrtc/pc/channelmanager.h
index 68b1ab2..15a3752 100644
--- a/webrtc/pc/channelmanager.h
+++ b/webrtc/pc/channelmanager.h
@@ -75,7 +75,7 @@
   void GetSupportedAudioSendCodecs(std::vector<AudioCodec>* codecs) const;
   void GetSupportedAudioReceiveCodecs(std::vector<AudioCodec>* codecs) const;
   void GetSupportedAudioRtpHeaderExtensions(RtpHeaderExtensions* ext) const;
-  std::vector<VideoCodec> GetSupportedVideoCodecs() const;
+  void GetSupportedVideoCodecs(std::vector<VideoCodec>* codecs) const;
   void GetSupportedVideoRtpHeaderExtensions(RtpHeaderExtensions* ext) const;
   void GetSupportedDataCodecs(std::vector<DataCodec>* codecs) const;