Reland of Delete cricket::VideoFrame::GetTimeStamp. (patchset #1 id:1 of https://codereview.webrtc.org/2306953002/ )

Reason for revert:
Will reland after downstream projects are updated.

Original issue's description:
> Revert of Delete cricket::VideoFrame::GetTimeStamp. (patchset #1 id:1 of https://codereview.webrtc.org/2305623002/ )
>
> Reason for revert:
> Broke downstream project.
>
> Original issue's description:
> > Delete cricket::VideoFrame::GetTimeStamp.
> >
> > TBR=tkchin@webrtc.org  # Trivial change to VideoRendererAdapter
> > BUG=webrtc:5682
> >
> > Committed: https://crrev.com/fd6c99e43137d01fa6c120f7160f7c2999d1d8a3
> > Cr-Commit-Position: refs/heads/master@{#14037}
>
> TBR=perkj@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:5682
>
> Committed: https://crrev.com/bca69e87de5df290f728833a4b3d8af3ae5d88e6
> Cr-Commit-Position: refs/heads/master@{#14038}

TBR=perkj@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:5682

Review-Url: https://codereview.webrtc.org/2310043002
Cr-Commit-Position: refs/heads/master@{#14089}

webrtc/sdk/objc/Framework/Classes/RTCVideoRendererAdapter.mm

@@ -30,7 +30,8 @@ class VideoRendererAdapter
     RTCVideoFrame* videoFrame = [[RTCVideoFrame alloc]
         initWithVideoBuffer:nativeVideoFrame.video_frame_buffer()
                    rotation:nativeVideoFrame.rotation()
-                timeStampNs:nativeVideoFrame.GetTimeStamp()];
+                timeStampNs:nativeVideoFrame.timestamp_us() *
+                                rtc::kNumNanosecsPerMicrosec];
     CGSize current_size = (videoFrame.rotation % 180 == 0)
                               ? CGSizeMake(videoFrame.width, videoFrame.height)
                               : CGSizeMake(videoFrame.height, videoFrame.width);