[NaCl SDK Docs] Only generate one top-level <section> element.

[NaCl SDK Docs] Only generate one top-level <section> element.

This fixes the right-side table-of-contents on the documentation page, so it is
collapsible and only shows h2 headings by default.

NOTRY because it is a documentation-only change.

BUG=374811
R=sbc@chromium.org
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=287804

[binji, 2014-08-05 23:22:05]

+jfb

[JF, 2014-08-05 23:26:48]

lgtm

[binji, 2014-08-05 23:32:43]

The CQ bit was checked by binji@chromium.org

[commit-bot: I haz the power, 2014-08-05 23:36:41]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/binji@chromium.org/438403003/1

[commit-bot: I haz the power, 2014-08-05 23:36:41]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-05 23:36:42]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Sam Clegg, 2014-08-06 17:48:32]

lgtm

[binji, 2014-08-06 17:58:31]

The CQ bit was checked by binji@chromium.org

[commit-bot: I haz the power, 2014-08-06 17:59:47]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/binji@chromium.org/438403003/1

[commit-bot: I haz the power, 2014-08-06 18:01:50]

Change committed as 287804