Change default content verification mode for Google Chrome builds

Change default content verification mode for Google Chrome builds

It's been configured to be set to 'enforce' mode via the server-side
experiment for quite a while, so it makes sense to have it turned on by
default in the code as well.

BUG=526873
Committed: https://crrev.com/d522554d6554e461249a0041716d1574cb34e3e3
Cr-Commit-Position: refs/heads/master@{#346552}

[asargent_no_longer_on_chrome, 2015-08-31 23:55:50]

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

[Ken Rockot(use gerrit already), 2015-09-01 00:01:22]

lgtm

[asargent_no_longer_on_chrome, 2015-09-01 00:13:40]

The CQ bit was checked by asargent@chromium.org

[commit-bot: I haz the power, 2015-09-01 00:14:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1307103003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1307103003/1

[commit-bot: I haz the power, 2015-09-01 01:38:35]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-01 01:39:06]

Patchset 1 (id:??) landed as
https://crrev.com/d522554d6554e461249a0041716d1574cb34e3e3
Cr-Commit-Position: refs/heads/master@{#346552}