Fix the value of the first byte of nal unit generated by fake H.264 encoder.
Fix the value of the first byte of nal unit
generated by fake H.264 encoder.

BUG=
R=kjellander@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/38849004

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8253}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: e69220ca84e4e63b79c1c1faa9872f42850a3a4a

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