Revert of Delete Rtx-related methods from RTPPayloadRegistry. (patchset #3 id:40001 of https://codereview.webrtc.org/3006993002/ )

Reason for revert:
This has to be reverted to enable reverting cl https://codereview.webrtc.org/3006063002/, which seems to have broken ulpfec.

Original issue's description:
> Delete Rtx-related methods from RTPPayloadRegistry.
>
> Delete methods IsRtx, IsEncapsulated and RestoreOriginalPacket.
>
> BUG=webrtc:7135
>
> Review-Url: https://codereview.webrtc.org/3006993002
> Cr-Commit-Position: refs/heads/master@{#19739}
> Committed: https://chromium.googlesource.com/external/webrtc/+/5b4b52264132eefba10bc6880871715f9692da90

TBR=stefan@webrtc.org,danilchap@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:7135

Review-Url: https://codereview.webrtc.org/3011093002
Cr-Commit-Position: refs/heads/master@{#19742}
7 files changed
tree: 0433cc190db70d0af67e5f45ba7eaf47ac6e083f
  1. .clang-format
  2. .git-blame-ignore-revs
  3. .gitignore
  4. .gn
  5. .vpython
  6. AUTHORS
  7. BUILD.gn
  8. CODE_OF_CONDUCT.md
  9. DEPS
  10. LICENSE
  11. LICENSE_THIRD_PARTY
  12. OWNERS
  13. PATENTS
  14. PRESUBMIT.py
  15. README.md
  16. WATCHLISTS
  17. build_overrides/
  18. codereview.settings
  19. data/
  20. infra/
  21. license_template.txt
  22. pylintrc
  23. resources/
  24. style-guide.md
  25. tools_webrtc/
  26. webrtc/
README.md

WebRTC is a free, open software project that provides browsers and mobile applications with Real-Time Communications (RTC) capabilities via simple APIs. The WebRTC components have been optimized to best serve this purpose.

Our mission: To enable rich, high-quality RTC applications to be developed for the browser, mobile platforms, and IoT devices, and allow them all to communicate via a common set of protocols.

The WebRTC initiative is a project supported by Google, Mozilla and Opera, amongst others.

Development

See http://www.webrtc.org/native-code/development for instructions on how to get started developing with the native code.

More info