Update {virtual,override,final} to follow C++11 style in extensions, round 2.

Update {virtual,override,final} to follow C++11 style in extensions, round 2.

The Google style guide states that only one of {virtual,override,final}
should be used for each declaration, since override implies virtual and
final implies both virtual and override.

This patch was automatically generated with a ChromeOS build using a
variation of https://codereview.chromium.org/598073004.

BUG=417463
Committed: https://crrev.com/6c4f4ee156220fa7b058456d536d4e6e7f9b5d61
Cr-Commit-Position: refs/heads/master@{#312737}

[dcheng, 2015-01-22 22:32:17]

dcheng@chromium.org changed reviewers:
+ scheib@chromium.org

[scheib, 2015-01-22 23:03:55]

lgtm

[dcheng, 2015-01-22 23:06:42]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2015-01-22 23:09:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/873473003/1

[commit-bot: I haz the power, 2015-01-23 01:12:35]

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

[commit-bot: I haz the power, 2015-01-23 01:12:36]

Exceeded time limit waiting for builds to trigger.

[dcheng, 2015-01-23 01:14:32]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2015-01-23 01:17:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/873473003/1

[commit-bot: I haz the power, 2015-01-23 01:44:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-23 01:46:11]

Patchset 1 (id:??) landed as
https://crrev.com/6c4f4ee156220fa7b058456d536d4e6e7f9b5d61
Cr-Commit-Position: refs/heads/master@{#312737}