Remove unused constant history::kThumbnailsFilename.

Remove unused constant history::kThumbnailsFilename.

The migration from Thumbnails to Favicons has been done for many years.

BUG=617226
Committed: https://crrev.com/f06ded49f7565b24afc3005c395dc222774e6244
Cr-Commit-Position: refs/heads/master@{#397951}

[Scott Hess - ex-Googler, 2016-06-03 21:27:00]

shess@chromium.org changed reviewers:
+ sky@chromium.org

[Scott Hess - ex-Googler, 2016-06-03 21:27:00]

The diagnostics code was the last real user!

[Scott Hess - ex-Googler, 2016-06-03 21:27:15]

On 2016/06/03 21:27:00, Scott Hess wrote:
> The diagnostics code was the last real user!

[See "depends on" patchset.]

[sky, 2016-06-03 22:33:17]

LGTM

[Scott Hess - ex-Googler, 2016-06-05 20:29:06]

The CQ bit was checked by shess@chromium.org

[commit-bot: I haz the power, 2016-06-05 20:29:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2040553002/1

[commit-bot: I haz the power, 2016-06-05 21:39:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-06-05 21:41:04]

Description was changed from

==========
Remove unused constant history::kThumbnailsFilename.

The migration from Thumbnails to Favicons has been done for many years.

BUG=617226
==========

to

==========
Remove unused constant history::kThumbnailsFilename.

The migration from Thumbnails to Favicons has been done for many years.

BUG=617226

Committed: https://crrev.com/f06ded49f7565b24afc3005c395dc222774e6244
Cr-Commit-Position: refs/heads/master@{#397951}
==========

[commit-bot: I haz the power, 2016-06-05 21:41:05]

Patchset 1 (id:??) landed as
https://crrev.com/f06ded49f7565b24afc3005c395dc222774e6244
Cr-Commit-Position: refs/heads/master@{#397951}