App list folder icons: Fixed off-by-one error.

App list folder icons: Fixed off-by-one error.

Not actually visible to the user. It is not supposed to regenerate the
icon if the fifth or greater item changed. Due to an off-by-one error,
it would still regenerate the icon if the fifth item changed (which is
unnecessary).

NB: Tests are incoming (which would have caught this error).

Also harden a DCHECK (fixing a similar off-by-one error, and making it
into a CHECK because it would be a security issue if it failed).

BUG=425444
Committed: https://crrev.com/d1a3882d53bf5a765fb6b19fa0da54b265570e31
Cr-Commit-Position: refs/heads/master@{#302030}

[Matt Giuca, 2014-10-29 07:00:13]

mgiuca@chromium.org changed reviewers:
+ calamity@chromium.org

[calamity, 2014-10-30 03:23:31]

lgtm

[Matt Giuca, 2014-10-30 03:30:04]

The CQ bit was checked by mgiuca@chromium.org

[commit-bot: I haz the power, 2014-10-30 03:30:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/681373004/20001

[commit-bot: I haz the power, 2014-10-30 04:14:16]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-10-30 04:15:10]

Patchset 2 (id:??) landed as
https://crrev.com/d1a3882d53bf5a765fb6b19fa0da54b265570e31
Cr-Commit-Position: refs/heads/master@{#302030}