Add the capturer timestamp as a parameter in VEA::BitstreamBufferReady() so
RTCVideoEncoder can use it.

BUG=350106
TEST=Verify that apprtc loopback works on minnie.
R=bbudge@chromium.org, posciak@chromium.org, sandersd@chromium.org, wfh@chromium.org, wuchengli@chromium.org

Review-Url: https://codereview.chromium.org/1996453003
Cr-Commit-Position: refs/heads/master@{#396786}