Reland of StartTimestamp generated randomly in RtpSender constructor

Reland of StartTimestamp generated randomly in RtpSender constructor (patchset #1 id:1 of https://codereview.webrtc.org/2248413002/ )

Reason for revert:
Reland: downstream code expectation about rtp_sender timestamp adjusted.

Original issue's description:
> Revert of StartTimestamp generated randomly in RtpSender constructor (patchset #4 id:60001 of https://codereview.webrtc.org/2241193002/ )
>
> Reason for revert:
> Breaks downstream code.
>
> Original issue's description:
> > StartTimestamp generated randomly in RtpSender constructor
> > instead of not-randomly at SetSendingState(true)
> > Renamed to timestamp_offset_ to better match meaning of the variable.
> >
> > R=asapersson@webrtc.org, terelius@webrtc.org
> >
> > Committed: https://crrev.com/4466782ae43e1b1125a55ee7e18abd10dd37cede
> > Cr-Commit-Position: refs/heads/master@{#13796}
>
> TBR=asapersson@webrtc.org,terelius@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
>
> Committed: https://crrev.com/86c96948e340cf8b879bddb0c7293f3b5ad4dad4
> Cr-Commit-Position: refs/heads/master@{#13798}

TBR=asapersson@webrtc.org,terelius@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/71fead2146b6895d4d04c3f4c2a8eb465b2c5881
Cr-Commit-Position: refs/heads/master@{#13811}

[danilchap, 2016-08-18 09:01:38]

The CQ bit was checked by danilchap@webrtc.org

[danilchap, 2016-08-18 09:01:39]

Created Reland of StartTimestamp generated randomly in RtpSender constructor

[commit-bot: I haz the power, 2016-08-18 09:01:43]

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, 2016-08-18 09:01:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-08-18 09:02:26]

Description was changed from

==========
Reland of StartTimestamp generated randomly in RtpSender constructor (patchset
#1 id:1 of https://codereview.webrtc.org/2248413002/ )

Reason for revert:
Reland: downstream code expectation about rtp_sender timestamp adjusted.

Original issue's description:
> Revert of StartTimestamp generated randomly in RtpSender constructor (patchset
#4 id:60001 of https://codereview.webrtc.org/2241193002/ )
> 
> Reason for revert:
> Breaks downstream code.
> 
> Original issue's description:
> > StartTimestamp generated randomly in RtpSender constructor
> > instead of not-randomly at SetSendingState(true)
> > Renamed to timestamp_offset_ to better match meaning of the variable.
> >
> > R=asapersson@webrtc.org, terelius@webrtc.org
> >
> > Committed: https://crrev.com/4466782ae43e1b1125a55ee7e18abd10dd37cede
> > Cr-Commit-Position: refs/heads/master@{#13796}
> 
> TBR=asapersson@webrtc.org,terelius@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> 
> Committed: https://crrev.com/86c96948e340cf8b879bddb0c7293f3b5ad4dad4
> Cr-Commit-Position: refs/heads/master@{#13798}

TBR=asapersson@webrtc.org,terelius@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
==========

to

==========
Reland of StartTimestamp generated randomly in RtpSender constructor (patchset
#1 id:1 of https://codereview.webrtc.org/2248413002/ )

Reason for revert:
Reland: downstream code expectation about rtp_sender timestamp adjusted.

Original issue's description:
> Revert of StartTimestamp generated randomly in RtpSender constructor (patchset
#4 id:60001 of https://codereview.webrtc.org/2241193002/ )
>
> Reason for revert:
> Breaks downstream code.
>
> Original issue's description:
> > StartTimestamp generated randomly in RtpSender constructor
> > instead of not-randomly at SetSendingState(true)
> > Renamed to timestamp_offset_ to better match meaning of the variable.
> >
> > R=asapersson@webrtc.org, terelius@webrtc.org
> >
> > Committed: https://crrev.com/4466782ae43e1b1125a55ee7e18abd10dd37cede
> > Cr-Commit-Position: refs/heads/master@{#13796}
>
> TBR=asapersson@webrtc.org,terelius@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
>
> Committed: https://crrev.com/86c96948e340cf8b879bddb0c7293f3b5ad4dad4
> Cr-Commit-Position: refs/heads/master@{#13798}

TBR=asapersson@webrtc.org,terelius@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/71fead2146b6895d4d04c3f4c2a8eb465b2c5881
Cr-Commit-Position: refs/heads/master@{#13811}
==========

[commit-bot: I haz the power, 2016-08-18 09:02:27]

Patchset 1 (id:??) landed as
https://crrev.com/71fead2146b6895d4d04c3f4c2a8eb465b2c5881
Cr-Commit-Position: refs/heads/master@{#13811}