Added support for keeping a buffer of the previous X seconds, to add to an AcmDump.

In addition, timestamps are now absolute instead of relative to LOG_START.

BUG=webrtc:4741
R=henrik.lundin@webrtc.org, kwiberg@webrtc.org, stefan@webrtc.org, terelius@webrtc.org

Review URL: https://codereview.webrtc.org/1209563002.

Cr-Commit-Position: refs/heads/master@{#9509}
2 files changed