Change capture time format to nanoseconds in EncodedImage.

The millisecond field is deprecated and will be removed once the
dependencies have been updated.

BUG=webrtc:7760

Review-Url: https://codereview.webrtc.org/3010623002
Cr-Original-Commit-Position: refs/heads/master@{#19622}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: e172d89f73775d81fa72d8aa18604fec30ce60d9
6 files changed