Revert "Use the factory instead of using the builtin code path in `VideoCodecInitializer`."

This reverts commit be142178aaf6ab4089b4d81c88c3d59c12cca567.

Reason for revert: breaking internal projects

Original change's description:
> Use the factory instead of using the builtin code path in `VideoCodecInitializer`.
> 
> Bug: webrtc:9513
> Change-Id: Ia299ae1044a3ff4c91e208200938cba540bdcea6
> Reviewed-on: https://webrtc-review.googlesource.com/c/94782
> Commit-Queue: Jiawei Ou <ouj@fb.com>
> Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
> Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
> Reviewed-by: Sebastian Jansson <srte@webrtc.org>
> Reviewed-by: Anders Carlsson <andersc@webrtc.org>
> Reviewed-by: Seth Hampson <shampson@webrtc.org>
> Reviewed-by: Erik Språng <sprang@webrtc.org>
> Reviewed-by: Niels Moller <nisse@webrtc.org>
> Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#25456}

TBR=brandtr@webrtc.org,magjed@webrtc.org,sakal@webrtc.org,nisse@webrtc.org,andersc@webrtc.org,tommi@webrtc.org,kthelgason@webrtc.org,sprang@webrtc.org,srte@webrtc.org,perkj@webrtc.org,tkchin@webrtc.org,shampson@webrtc.org,glaznev@webrtc.org,ouj@fb.com,qingsi@webrtc.org

Change-Id: I8040ccabe3ae6464d72c7696adb663c1dd275b63
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:9513
Reviewed-on: https://webrtc-review.googlesource.com/c/108980
Reviewed-by: Qingsi Wang <qingsi@webrtc.org>
Commit-Queue: Qingsi Wang <qingsi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25459}
diff --git a/modules/video_coding/include/video_codec_initializer.h b/modules/video_coding/include/video_codec_initializer.h
index e979f9c..ee70810 100644
--- a/modules/video_coding/include/video_codec_initializer.h
+++ b/modules/video_coding/include/video_codec_initializer.h
@@ -30,9 +30,15 @@
   // type used. For instance, VP8 will create an allocator than can handle
   // simulcast and temporal layering.
   // GetBitrateAllocator is called implicitly from here, no need to call again.
-  static bool SetupCodec(const VideoEncoderConfig& config,
-                         const std::vector<VideoStream>& streams,
-                         VideoCodec* codec);
+  static bool SetupCodec(
+      const VideoEncoderConfig& config,
+      const std::vector<VideoStream>& streams,
+      VideoCodec* codec,
+      std::unique_ptr<VideoBitrateAllocator>* bitrate_allocator);
+
+  // Create a bitrate allocator for the specified codec.
+  static std::unique_ptr<VideoBitrateAllocator> CreateBitrateAllocator(
+      const VideoCodec& codec);
 
  private:
   static VideoCodec VideoEncoderConfigToVideoCodec(