Update {virtual,override} to follow C++11 style in base.

Update {virtual,override} to follow C++11 style in base.

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 manually generated using a regex and a text editor.

BUG=417463
Committed: https://crrev.com/c0b00106efe0a3737148de518b77ba8273417e69
Cr-Commit-Position: refs/heads/master@{#326392}

[ncarter (slow), 2015-04-22 21:05:21]

nick@chromium.org changed reviewers:
+ thestig@chromium.org

[Lei Zhang, 2015-04-22 21:06:49]

lgtm

[ncarter (slow), 2015-04-22 21:15:20]

The CQ bit was checked by nick@chromium.org

[commit-bot: I haz the power, 2015-04-22 21:16:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1094903006/1

[commit-bot: I haz the power, 2015-04-22 23:17:26]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-22 23:18:22]

Patchset 1 (id:??) landed as
https://crrev.com/c0b00106efe0a3737148de518b77ba8273417e69
Cr-Commit-Position: refs/heads/master@{#326392}