Proto commits in google/securemessage

These 2 commits are when the Protocol Buffers files have changed:

Commit:e7b6988
Author:Alexey Polyudov
Committer:Alexey Polyudov

Bring up-to-date with internal code Signed-off-by: Alexey Polyudov <apolyudov@google.com> Change-Id: I86c64d081912f6a03c0bd86d706e8ccedf350978

The documentation is generated from this commit.

Commit:f8f6b36
Author:Alexei Czeskis

initial addition of C++ implementation