Make some fields non-nullable in serial.mojom and data_stream.mojom.

Make some fields non-nullable in serial.mojom and data_stream.mojom.

This also removes some null checks for the now non-nullable fields.

BUG=407683
Committed: https://crrev.com/da421fab9270e9fd48875f14e3ae9a001c6f0d77
Cr-Commit-Position: refs/heads/master@{#294277}

[Sam McNally, 2014-09-10 08:01:33]

Patchset #1 (id:1) has been deleted

[Sam McNally, 2014-09-10 08:07:10]

sammc@chromium.org changed reviewers:
+ rockot@chromium.org

[Ken Rockot(use gerrit already), 2014-09-10 16:32:40]

lgtm

[Sam McNally, 2014-09-10 23:24:18]

The CQ bit was checked by sammc@chromium.org

[commit-bot: I haz the power, 2014-09-10 23:50:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/562563002/20001

[commit-bot: I haz the power, 2014-09-11 00:53:29]

Committed patchset #1 (id:20001) as d5d337f07bc4b224f4c9bdecb5429875cb4e939a

[commit-bot: I haz the power, 2014-09-11 00:55:51]

Patchset 1 (id:??) landed as
https://crrev.com/da421fab9270e9fd48875f14e3ae9a001c6f0d77
Cr-Commit-Position: refs/heads/master@{#294277}