Explicitly set test_proto.proto's syntax.

Explicitly set test_proto.proto's syntax.

No behavior change, but new protobuf versions warn about the absence of this
line and all other our .proto files have it.

BUG=525255
Committed: https://crrev.com/869255adad624761c098b6e3508b66d5f178a628
Cr-Commit-Position: refs/heads/master@{#346007}

[Nico, 2015-08-27 20:08:15]

thakis@chromium.org changed reviewers:
+ satorux@chromium.org

[satorux1, 2015-08-27 22:16:27]

lgtm!

[Nico, 2015-08-27 22:17:55]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2015-08-27 22:18:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1318083004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1318083004/1

[commit-bot: I haz the power, 2015-08-27 22:24:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-27 22:24:37]

Patchset 1 (id:??) landed as
https://crrev.com/869255adad624761c098b6e3508b66d5f178a628
Cr-Commit-Position: refs/heads/master@{#346007}