Added various timestamps to FrameObject.

Added various timestamps to the FrameObject class which are needed to calculate
the jitter delay.

BUG=webrtc:5514

Review-Url: https://codereview.webrtc.org/2124943002
Cr-Original-Commit-Position: refs/heads/master@{#13434}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: b4d31085b4534988ee37a4f2ed680a9ed1b34218
6 files changed