Revert of Completed the functionalities of SrtpTransport.

Revert of Completed the functionalities of SrtpTransport. (patchset #7 id:320001 of https://codereview.webrtc.org/2997983002/ )

Reason for revert:
This seems to be causing some video freezes. See https://bugs.chromium.org/p/webrtc/issues/detail?id=8251

Original issue's description:
> Completed the functionalities of SrtpTransport.
> 
> The SrtpTransport takes the SRTP responsibilities from the BaseChannel
> and SrtpFilter. SrtpTransport is now responsible for setting the crypto
> keys, protecting and unprotecting the packets. SrtpTransport doesn't know
> if the keys are from SDES or DTLS handshake.
> 
> BaseChannel is now only responsible setting the offer/answer for SDES 
> or extracting the key from DtlsTransport and configuring the 
> SrtpTransport.
> 
> SrtpFilter is used by BaseChannel as a helper for SDES negotiation.
> 
> BUG=webrtc:7013
> 
> Review-Url: https://codereview.webrtc.org/2997983002
> Cr-Commit-Position: refs/heads/master@{#19636}
> Committed: https://chromium.googlesource.com/external/webrtc/+/e683c6871fef24d3ff64f085d6bc0e965f17fcf7

TBR=deadbeef@webrtc.org,pthatcher@google.com,zhihuang@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:7013

[sprang_webrtc, 2017-09-15 08:53:17]

The CQ bit was checked by sprang@webrtc.org

[sprang_webrtc, 2017-09-15 08:53:17]

Created Revert of Completed the functionalities of SrtpTransport.

[commit-bot: I haz the power, 2017-09-15 08:53:22]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.webrtc.org/...

[commit-bot: I haz the power, 2017-09-15 08:56:31]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-09-15 08:56:33]

Try jobs failed on following builders:
  mac_compile_dbg on master.tryserver.webrtc (JOB_FAILED,
http://build.chromium.org/p/tryserver.webrtc/builders/mac_compile_dbg/builds/...)
  presubmit on master.tryserver.webrtc (JOB_FAILED,
http://build.chromium.org/p/tryserver.webrtc/builders/presubmit/builds/21687)

[Zhi Huang, 2017-09-21 17:54:14]

Description was changed from

==========
Revert of Completed the functionalities of SrtpTransport. (patchset #7 id:320001
of https://codereview.webrtc.org/2997983002/ )

Reason for revert:
This seems to be causing some video freezes. See
https://bugs.chromium.org/p/webrtc/issues/detail?id=8251

Original issue's description:
> Completed the functionalities of SrtpTransport.
> 
> The SrtpTransport takes the SRTP responsibilities from the BaseChannel
> and SrtpFilter. SrtpTransport is now responsible for setting the crypto
> keys, protecting and unprotecting the packets. SrtpTransport doesn't know
> if the keys are from SDES or DTLS handshake.
> 
> BaseChannel is now only responsible setting the offer/answer for SDES 
> or extracting the key from DtlsTransport and configuring the 
> SrtpTransport.
> 
> SrtpFilter is used by BaseChannel as a helper for SDES negotiation.
> 
> BUG=webrtc:7013
> 
> Review-Url: https://codereview.webrtc.org/2997983002
> Cr-Commit-Position: refs/heads/master@{#19636}
> Committed:
https://chromium.googlesource.com/external/webrtc/+/e683c6871fef24d3ff64f085d...

TBR=deadbeef@webrtc.org,pthatcher@google.com,zhihuang@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:7013
==========

to

==========
Revert of Completed the functionalities of SrtpTransport. (patchset #7 id:320001
of https://codereview.webrtc.org/2997983002/ )

Reason for revert:
This seems to be causing some video freezes. See
https://bugs.chromium.org/p/webrtc/issues/detail?id=8251

Original issue's description:
> Completed the functionalities of SrtpTransport.
> 
> The SrtpTransport takes the SRTP responsibilities from the BaseChannel
> and SrtpFilter. SrtpTransport is now responsible for setting the crypto
> keys, protecting and unprotecting the packets. SrtpTransport doesn't know
> if the keys are from SDES or DTLS handshake.
> 
> BaseChannel is now only responsible setting the offer/answer for SDES 
> or extracting the key from DtlsTransport and configuring the 
> SrtpTransport.
> 
> SrtpFilter is used by BaseChannel as a helper for SDES negotiation.
> 
> BUG=webrtc:7013
> 
> Review-Url: https://codereview.webrtc.org/2997983002
> Cr-Commit-Position: refs/heads/master@{#19636}
> Committed:
https://chromium.googlesource.com/external/webrtc/+/e683c6871fef24d3ff64f085d...

TBR=deadbeef@webrtc.org,pthatcher@google.com,zhihuang@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:7013
==========