video_coding::PacketBuffer now group all H264 packets with the same timestamp into the same frame.
video_coding::PacketBuffer now group all H264 packets with the same timestamp into the same frame.

Since we can't know when a H264 frame really starts we instead group all packets together by timestamp when a frame seems to be complete (only in the case of H264).

BUG=webrtc:5514

Review-Url: https://codereview.webrtc.org/2675693002
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#16419}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 8c61924b5671b568a1953820961e4ec24e19e4c6

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